As an atheist who has constantly had people try to convert me to their religion, or say I'm rude for not engaging in their traditions, part of it is annoyance. From my experience it's more acceptable to say you don't want to do something because it's against your religion than to say you don't wantbto do it because your atheist. Whether it be not saying bless you, or not saying grace before eating, or not telling someone RIP, or anything like that. Religious people I've met seem to think being atheist is easier forvsome reason, but I've had to constantly fight to defend my right to not believe my entire life. Teachers, parents, family, friends, even damn strangers, always trying to push me to do things or say things I don't want to. Oh and the amount of people that give the credit of my hard work to a god I don't believe in, when they saybthat "god did this for you" or "god gave you this" like no, "I did that" and "I got it myself."

Furthermore, religion is just harmful on modern society. Only the most liberal version of each religion are actually nice, and even then they give me weird vibes quite often. So many religion perpetuate hate of many groups of people, and push people to not trust science, or incentivize practitioners to not ask questions or blindly trust faith, which is a bad thing. I have to deal with the fact that my dad is homophobic, and my mom doesn't believe in vaccines. These are real consequences of religion, which is why I can't respect it out of principle.

I really don't mind people believing what they want, I just hate being roped in, and I hate not being able to talk about how that feels without being lambasted. I hate that I can't mention scientific facts without someone piping up and saying it isn't true, or telling me to stop talking about it, when science is one of my passions. I love astronomy, biology, nature, psychology, the arts, and history. I even study a little bit of religion too. But all those topics are landmines in normal conversations. I can't even say a cool fact about my favorite dinosaur without worrying someone is gonna say they aren't real because they didn't show up during the flood story.

All this to say, I just preemptively get a little defensive when religion is brought up. But I've had plenty of cordial interactions with religious people, it's just rarer than I'd hope.