Regarding singular they, it's not the word "they" that annoys me.

I really don’t understand what the big deal is with all of this (in most cases)

No, in general, you wouldn’t, but that’s not where you’d use it. In the ‘past’ you’d use it if you didn’t know who it was. What’s being proposed is that you use it when you don’t know (or haven’t been told) if the person is a male or female. Or rather, what pronoun the person what’s to be referred to as.

You wouldn’t say it there because the pronoun has already been identified as ‘he’. However, again in the ‘past’, if you didn’t know who was going to pick it up there would be no problem with saying ‘they’ll be here in a minute, just give it to them when they arrive’. No one would bat an eye at that sentence, you’re saying it because you don’t know who’s picking it up. Sam? Marie? And now, the trans community is asking us to use they until we’ve been the person has told use how they want to be called. He/she/they.
Mostly not a big deal, though sometimes I think they go a bit overboard. For example, most people are not going to work on the assumption that everyone might be trans and/or not be okay with someone calling them by the pronoun they present as. That is, if a random stranger comes up to me, and she looks female, you can call it cissexist, but I’m going to refer to her with female pronouns unless I’m told differently. As a society, I don’t think we’re ready (and in fact, I think most/many people would actually be offended) if we asked them if they were male/female upon meeting them. At least in general.

In one case I heard it referred to as cissexist to ask a pregnant person if they’re having a boy or girl…wait for it…because we can’t know until the child is old enough to decide for itself what it wants to be called (this was in all seriousness).
I’m all for whatever, I’ll call you whatever you want to be called, but IMO, something like this is almost looking for things to be offended by and forcing the divide to be wider than it needs to be. Acceptance of the LGBT+ community, I thought, was doing very well, but in the last year or so, it seems like some people are purposely making it difficult. It almost seems like it’s gone from ‘thanks for accepting us, here’s something else you can do/do you have any questions/etc’ to ‘if you’re not us, you’re actively against us’.
I understand the sentiment in a lot of the cases, but I think a lot of people that are very accepting are going to get pushed back. I think a lot of those people that get yelled at for saying the wrong thing without realizing it are eventually going to think 'I tried and I worked and I changed and still everything I do or say is wrong and oppressive and turns into a fight, I’ll move on, '.

Anyways, getting back to the they thing:
TL;DR For all your life, if you were referring to someone and you didn’t know their gender, you said ‘they’. That’s all you’re being asked to do now. The only difference is that before you usually didn’t know their gender because you couldn’t see them, now you don’t know their gender even though you can see them. Same ‘they’, they’re just standing closer to you.

Before:
Who’s umbrella is this?
My friend’s, it’s getting picked up later
Great, give them this coat too, it’s cold out.

Now:
Who’s umbrella is this?
Pat’s, over there.
Great, I’ll give it to them.

PS, I’m really debating even hitting submit. I feel like I’m going to end up with a PM at some point telling me I’m either totally wrong, I’m not LGBT so I shouldn’t talk about it or I’m going to get yelled at for having any kind of opinion.

I say that never in the history of any language has a top-down attempt to change a comfortable, workable usage succeeded. Individual words are the Cirque du Soleil performers of linguistics: they are incredibly flexible in their meanings.

Rather than trying to force everyone to attach “is” to “they,” which sounds awful to most ears, why not recognize that “are” has an additional definition? You already know about:

  1. The third person plural conjugation of “be”
  2. The second person singular conjugation of “be”
  3. The first person plural conjugation of “be”
  4. The second person plural conjugation of “be”

Recognize that there’s one more definition:

  1. The third person singular gender-nonspecific conjugation of “be”

This definition has been around for hundreds of years. It’s nothing new.

I think “they is” vs. “they are” is a distinction without a need. We use “are” with both the singular and plural version of “you” and it’s clear through context, typically, it’s the same with singular or plural versions of “they” as well. Personally, I’m not a huge fan of the “they” construction, as I don’t really see what’s so bad with defaulting to one gender which is perfectly fine in other languages. Regardless, I think the “they” battle is essentially over and I find myself using it often enough. My only real complaint would be like the example in the OP of “Where’s Sam?” “They are over there.” Chances are, if you know who Sam is, you know whether it should be he or she, so it just seems unnecessarily ambiguous to use “they” when an appropriate singular pronoun can be used.

And yes, I would have prefered a gender neutral pronoun, but the problem is, things like “ze” and “hir” were never going to work precisely because they were constructed and unnatural and there’s just too much resistance against just letting “he” or “she” be the default when gender is indeterminent. So, really, it just seems like “they” is ultimately the least bad alternative.

That said, the one construction that I do find myself using that makes sense to me is “themself” vs. “themselves” as touched on in the OP. I won’t say “they is” but it does make sense not to unnecessarily pluralize the reflex. So, yes, I would say “they are all by themself” works fine for me.

Thank you for the correction! Indeed that would be the correct analogy.

I look to a future where the Act of Pronoun Clarification will replace business cards in the greeting process. “And how will we be addressed during this exchange?”

My kids travel in circles with several They’s. Close friends; students in AP classes. They tend to be accepting, and try to listen for what the person prefers.

Gender fluidity, like social media and living online, are an assumed part of this current generation.

Actually, you was the plural accusative (or objective) pronoun. The plural nominative was ye. You taking over the 2nd person is like if everyone started saying us instead of "I’, “me”, and “we”.

But note that the change above took a long time to happen. Over a hundred years. That’s because pronouns are among the most conservative parts of a language. This is why attempts to manufacture new gender-neutral pronouns have all been total failures.

The future is now. “Preferred gender pronouns” (or PGPs) are already part of introductions in some academic settings. It would be stretch to say this is across the board, but it’s becoming more typical in environments that have an element of identify-based focus. So if you are ever in a meeting where the chair says “let’s go around and introduce ourselves, what offices we are from, and our PGPs,” you are expected to say “hello, my name is Delphica, I’m from the Budget department, and my PGPs are she/her.” (or, you know, your own name and PGPs)

That’s a perfectly cromulent use of “We” when “We” happens to be The Crown. It’s called the “royal we” or “majestic plural”.