Agnostic here who was also confirmed (forced by parents) in catholicism. Christianity is just the most dominant religion in the culture, but there are different strains of it. The one I have found personally most irksome is southern evangelical/ non-denominational megachurches and the culture surrounding many of them. The main problem is that a lot of these people take it as their personal mission to try and convert people. It seems they're not truly comfortable until everyone else believes what they do.
I had first hand experience of this at A&M when some of the european international students I was friends with said people basically would trick them into going to this "cool event" that ended up being breakaway. I was pretty embarrassed to hear that, and usually apologetic that some of their first experiences at A&M were people trying to get them to go to church. It mirrors what I found when first moving to Texas where if you were white people always asked "what church do you go to?" very casually since they assume everyone is like them. This never happened to me growing up in the midwest.
I'd also contrast this with my wife's family who grew up episcopalian in the northeast. Her aunt runs summer camps at her church for kids, but would never seek to presume someone is religious or wouldn't try to convert them. Southern strains of christianity just seem so oriented towards conversion or getting everyone else to conform to your belief system. Maybe it's just because parts of the south are more homogenous in their makeup and less people are exposed to friends growing up who are jewish, muslim, etc.
Contrast that with judaism. I went to summer camp growing up where 98% of the other campers were jewish. No one would ever try to convert you to judaism. It's wonderful--they actively don't want to recruit you! In some ways it makes judaism more alluring, because it seems more exclusive.
