Pretty much.
Just about everything is a sin. Have you ever sat down and read this thing? Technically we’re not allowed to go to the bathroom.
I’m torn on this one.
While there is a lot of “never wrestle with a pig …” here, there’s also a knock-on effect that’s difficult to ignore.
To cite just one recent and glaring example: the “Stop the steal” grift has recruited an alarming number of stalwart and passionate believers.
And it is allowing a political party to institutionally rig coming elections.
And homophobia and other forms of bigotry attributed to (but not generally rooted in) religious doctrine can do profound harm to decent people who are just trying to live their lives.
While leaving these issues, and these people, as “free to hold their own beliefs” has its merits, there is widespread harm being done by sitting passively by and watching it happen.
None of which means that there’s a reliable and practicable way to get through, for reasons well enumerated by both @Velocity and @Ulfreida (among others).
I don’t see anything immoral or unethical here. At most, I see unkind or impolite. When debating stuff on FB, or elsewhere on the internet, you get a little more latitude than you would at a dinner party, because it’s easier for people who don’t want to participate in the discussion to leave.
In terms of strategy, I agree that such debates rarely change the mind of the person you’re debating. But even then, they might not be pointless. They may nudge an undecided observer toward your side, or give strength and courage to someone already on your side who wasn’t comfortable speaking up. But I do think it’s worth asking yourself from time to time what exactly you’re hoping to accomplish, and whether your actions have a reasonable probability of advancing that cause.
My rule of thumb with religion is:
If you expect your religion to improve the way you think and behave, more power to you.
If you expect your religion to make any alterations to me, then we’re going to have some frank words about that.
I don’t meddle around in people’s beliefs as long as they extend me the same courtesy.
Right: In a public venue (like Facebook), correcting misinformation or pointing out the clear flaw in a bad argument can influence “spectators” to a discussion, even if you can’t change the mind of the person you’re directly responding to.
(And just because it’s worth responding, that doesn’t mean it’s worth responding repeatedly when the person you’re responding to fails to be convinced.)
I don’t attempt to make a value judgement about someone’s religion (i.e. is it ‘good’, or ‘bad’ or ‘right’ or ‘wrong’), or about their beliefs in general. If someone wants to believe that the earth is 4000 or 6000 or less than a week (because the entire universe was created on Tuesday) then that’s fine with me as long as they aren’t trying to push that on me. There simply is no point in trying to convince someone against something they believe, regardless of if it’s religion or politics…people knows what they knows.
I will have a discussion with them about the specifics of their faith if they want to, or draw me into a discussion about stuff that can be verified, such as specific things in the bible(s) or religious doctrine I have a least some familiarity with. This can broaden to at least some history that I have some familiarization with, or even some basic science if they want to go there. I think sometimes people can be convinced that some of their ideas are not correct wrt what is actually in the bible or what their church official doctrine actually is…stuff that can often be trivially easy to find, it’s just that they haven’t bothered to even check and are going based on either their own uninformed notions or what some local preacher, pastor or priest is saying (sometimes it’s that they are only hearing what they want, sometimes it’s that these local fonts of supposed wisdom are clueless as well).
To me, “Correct Religious Folks” is more about correcting wrong ideas they have wrt their actual church doctrine or what’s in their religious texts than correcting them wrt trying to show them their faith at its core is wrong…that NEVER works out well, in my experience. Example…trying to explain to a Christian faithful that the Noah story just couldn’t have happened, scientifically, that there is zero evidence of it is a no-win situation. If they really believe the flood story happened then no amount of evidence is going to change their mind. However, explaining that, no, there was no mention of dinosaurs in the bible (any official version) is something that is beneficial (and, anecdotally, yes, I’ve had this exact discussion and the person was convinced in the end that, in fact, in no version of the bible, even using some rather loose translations from Greek, that had dinosaurs mentioned specifically in it 
).
Is that a fact?
In fact, it’s a…theory. 
Or, factually speaking, it could be a hypothesis. The fact is, I’m not actually sure…
Both are assholes in your unlikely scenario. The flat-earther and the person who couldn’t find a calmer way to make their points.
Unfortunately, some religions demand that you interfere in the lives of others, that you “save” them.
There’s a difference between “passively letting it happen” and wasting your time debating someone who you are never going to be able to convince.
IMO, the time you arguably have a duty to correct people’s mistaken and potentially dangerous beliefs is when you have some sort of relationship or history with them that makes them inclined to respect what you have to say. Many people have posted heartbreaking stories on this board about being unable to talk their own loved ones out of Trumpist lunacy; your chance of doing so with some stranger on the internet is zero.
(However, as others have said, the possibility that your arguments might persuade bystanders can certainly be in some cases a valid reason for pursuing such an argument)
And as pointed out, things like Flat Earth may not be explicitly declared in the text but rather be inferences made from what is. It becomes an argument about whether if the text includes things that are obvious figures of speech, does the choice of that figure of speech itself have the purpose of making a point and do we know what was the point being made.
There are all sorts of ways to “correct” religious folks. There’s the Pope’s way of castigating the less-than-humble including Vatican big-wigs, as summarized in this ABC News headline:
“Pope demands humility in new zinger-filled Christmas speech”
Or you could correct them Delbert Grady*-style.
*I once worked with a pathologist who bore a striking resemblance to Delbert Grady, both in looks and personality. 
In Dante Purgatory is located on the opposite side of the earth from Jerusalem, so he knew it was round way back then. However, I know a Flat Earther who believes it from being a literalist, but she also believes every CT out there.
I once came across something I liked:
Religion is like a penis.
It’s okay to have one, although not everybody does.
It’s okay to be proud of yours, although it’s not really an accomplishment.
It’s never okay to bring it out in front of unwilling participants or try to force it down somebody’s throat.
I just do my best to avoid getting into deep conversations about religion in the real word. The thing is even though I am not religious myself I have read books about the different faiths and even some lost faiths of history because I recognize the role religion has played as a cornerstone of humanity. So in a way there have been moments that I could have smugly ‘corrected’ religious folks but they weren’t causing me any bother so what’s the point.
Online discussions are another thing like on this forum. Things get more heated online in general but I’m speaking just in the real outside world.
Yes. This is something that non-evangelical people have a hard time grasping the importance of.
For evangelical sects, the duty to proselytize is paramount. You are saving souls from eternal torment in so doing. There is no greater moral imperative. I don’t see how they can bear living that way, frankly (and I know a couple of ex-evangelicals who have told me that this burden was an enormous relief to be free of).
Although this is, really, separate from a dogmatic adherence to easily-disproven “facts” – the existence of God or gods and his or their interest in the human race can neither be proven nor disproven – there is clearly some bleed over from one to the other.
My point is that you are almost as likely to convince someone that they shouldn’t try to save your soul from eternal torment as you are that the world is an orb.
I suppose if you like to argue, religion is a good thing to argue about.
I’m going to go against the grain on this thread and say I agree with the OP.
It’s fking weird that we’re in a world with such advanced technology that any person can communicate worldwide…and yet many people in the world’s wealthiest country use said technology to talk about a talking snake and other batshit stuff, from a book of obvious myths from the bronze age.
I guess at least it helped us with covid…oh that’s right religion did fuck all again, it’s been science helping us as usual.
I won’t bring up religion, but sure I’ll point out the flaws if anyone tries to bring it up, and that includes with Muslim friends and a close relative who is a minister.
Anyway, merry Christmas folks 