The perception of Christianity among people who don't identify with any religion or people who fall into more "liberal" circles has absolutely been tainted by sects/members of Christianity that do not at all represent the teachings in the Bible. There is justifiable resentment towards these groups that spills over into unjustifiable resentment towards Christians as a whole.
I can't count the number of times I've heard, living in California, either said directly to me by someone who didn't know I was Christian, overheard in a conversation, or discussed at some event completely out of pocket claims or insults towards Christianity that most people would find absolutely inappropriate to say about other groups.
It doesn't bother me because I understand where those people saying it are coming from. But it absolutely leads to the phenomenon of otherwise moderate or formerly left leaning Christians moving towards the group that doesn't wear their not so thinly veiled hate openly on their sleeves for something deeply personal and important in their lives. You are the company you keep and shifting over like this brings you more in line mentally overtime with the kind of people you don't want to emulate.
Rational or not rational, it just doesn't feel good as a human being to receive hate and disdain for something you consider an irreplaceable part of your life and worldview.
This doesn't apply solely to Christians and is really something the left has been doing for a long time and why it's been "losing" the propaganda war to the right and seeing so many people who formerly wouldn't want to associate with the kind of rhetoric found there today at least passively accepting it. Rhetoric of the left seems to far more often embrace (at least on a smaller scale between people) snark, putdowns, wholesale "intolerance" ie making individuals feel some combination of bad/guilty/stupid/backwards for "ignorant" views instead of engaging with them openly. The right uses an approach of playing the "reasonable" man that is open to discussion, support, of all views and then slowly getting people to get on board with the more radical ones.