Christian is a broad term, so I definitely have to concede the point that christian is a superset of fundamentalist christian, who are the real problem.
Many protestant sects have become accepting of homosexuality and even the pope is begrudgingly moving Catholicism away from uncivilized dogma.
Luther's reformation was ultimately about speaking truth to power. So I agree that there is a protestant disposition towards this type of thing or something in the protestant culture which is not as rotten as religions like orthodoxy or Islam. The idea of protestant work ethic, the golden rule, and similar artifacts probably played a very large part in the west out competing and out innovating the east.
However while I think there is an element of western culture that venerates speaking truth to power (and everything that implies, like there is a basis for finding truth), I don't think that is the christian element. If anything I think Socratic tradition is probably the root of western "enlightened" policies.
That being said, I am American and come from an American perspective. In America it is fundamentalist Christians who have largely opposed same sex marriage, even protestant cultures, my culture, were generally against homosexuality. For multiple elections it was a core wedge issue harped on like abortion. Some proponents of gay marriage are christian, but all opponents of gay marriage are christian (or Muslim, or some other fundamentalist or foreign group) and are against homosexuality because of their Christianity.
Fundamentalist is probably a better term.
After it became uncool to hate on homosexual people, there was a primarily christian shift to persecute transsexual people because they were weaker and less able to wield political power. I haven't seen the christian love movement pointed at trans people, that is for sure.
I read a pretty good quote about how the idea of separation between church and state was to protect the state from the church, but what are witnessing in real time is the state corrupting the church. These obviously non christian ideas of hate have somehow become the christian zeitgeist. The more christian someone feels, the more hate and lack of empathy for others they seem to have. Turn the other cheek isn't exactly republican dogma. Trump isn't exactly Christ like. I say this not as an outside judge. I say this having been raised Christian.
> The dig at Christianity is odd.
It is not a dig at Christianity. It is pointing out that the church wants to own the term spiritually and civic-ly. In other-words they want religious institutions that they have control over codified into law, and special privileges granted by the state over their codified religious institution. Separating the spiritual concept from the legal concept requires either the church give up the word marriage or the state give up the word marriage.
> state atheism
I am not sure I buy this idea of state atheism as presented. State atheism is forced. Western atheism is chosen. I think there is a world of difference, one has it's philosophical basis in reason, the other in dominance. Religion is dominance focused, you don't need to listen to much christian rock to hear how important submission to Jesus is, whatever that means. I also think the notion of state atheism in a palce like china is complicated. China cathol-isized bhuddism (meaning gutting the spiritual moral core and replacing it with indulgences and extravagance and other bankrupt practices while co-opting it as a tool of state power), while also seeing religion as a competitive force to state and as a colonial tool used by foreign powers.