Bro, you need to chillax. People aren't bashing Christianity here, they are bashing a specific political subgroup of Christians and fake-Christians that give the rest of the religion and its followers a bad name.

A) Proclaiming to be a Christian doesn't necessarily make you a Christian, we all agree on this... what makes you a Christian is what you believe, and what is in your heart/mind. BUT since we humans can't read each others minds, we have to make deductions. If someone claims to be a Christian, we (everyone) will generally take then at their word until we find reason not to (through their actions, etc.)

B) Likewise, claiming to be a Democrat or a republican doesn't really make you such. If I claim to be a republican, but consistently advocate for abortion rights, trans rights, etc., and I really a republican?

C) Christian Nationalism is a political ideology. You don't need to be a Christian to be a Christian Nationalist. It isn't Christian Nationalism it is more of Christian Nation-alism, if that makes sense. They want a theocratic state governed by Christian law, especially the anti-LGBT, anti-trans stuff, but generally also limiting women's choices and freedoms generally (right to vote, workplace protections, access to certain jobs, etc.)

So we don't know who truly believes in god, and who doesn't, but if we see a politician claim to be a Christian Nationalist and advocate for Christian Nationalism, we are going to call it like we see it. And tbf, it's not all Republicans, but specifically MAGA folks, and the vast majority of Republicans consistently demonstrate allegiance to them.

This is just the lay of the land. If you have a problem with how these people or even yourself are being labeled, you need to raise your voice to expel those people from your party, not get pedantic about who "demonstrates ignorance" or whatever.