I tend to avoid participating in religious v. atheist discussions online, and I don’t think I’ve ever precisely “debated” the issue online. There are a few times, here or there, where I’ve chimed in on a particular question or hypothetical exercise, and I’ve not been shy about my atheism, nor about the questions I have for people who have religious worldviews.
In real life I… tend to forget. I forget that people get all twisted about such things. I don’t forget that religion is important to many people, but somehow I forget just how intolerantly upset people can be. I think that comes from my environment growing up, where I can point to having had friends and neighbors who were Jewish, Catholic, Protestant (various flavors), Jehovah’s Witness, Jews for Jesus, Muslim, Buddhist, Hindu, Wiccan, Baha’i and atheist (and BTW, I can name the names I’m thinking of for each of those categories - it’s not just a list for listing’s sake), and never was I made aware of any conflict around the issue of differing religious beliefs (although I do recall a few scowls here and there from the Catholics, but no one was rude enough to make a real issue of it).
So, I blurt it out. If the conversation warrants, I’ll mention that I’m an atheist. In my adult life, I’ve been treated to glares, gasps, interrogations, and worse. It catches me off guard every time. I’ll be talking with a nice older lady, weather, hobbies, blah blah blah, and suddenly she’s angry with me, and I have to rewind a minute to realize she’s actually angry and threatened that I’m not a Presbyterian like she is.
So, from the point of view of the religious, and I mean only in particular the insulated religious who have not had the benefit of a cosmopolitan upbringing, I probably come across as a strident atheist in real life. When it comes up, that is.
In reading the OP, a few things come to mind for me. One is that there is a burgeoning atheist presence online (due to many factors, including the “New Atheists”, and /r atheism, the FFRF, etc). With increasing popularity comes increasing numbers of the lowest common denominator, i.e., assholes. My view on that is, it’s your turn. For years, decades, centuries, the non-Christians have had to put up with the lowest common denominator Christians spewing their lowest common denominator bullshit in the common square, and you’ll just have to get over the fact that you no longer have a monopoly on crappy people.
Also, something I especially note in regards to /r atheism (and other atheist forums)… it’s a club. You encounter a group of guys, and you’re bound to encounter some saucy language about women. Likewise, a group of women about men. Similarly, a group of atheists, speaking in a forum that is “theirs”, is likely to be a bit fast and loose with how they express themselves. For people who’ve been in primarily (their own) religious environments, this is shocking, and it feels rude and threatening. Time and time again, for instance, I have seen comments on how abrasive and, well, crappy /r atheism is, when, from my view, it’s just a bunch of guys like me talking about stuff from their point of view. It’s not usually profound or brilliant, mind, but it’s certainly not offensive… unless you expect it to be.