It's also worth noting that education is negatively correlated with religious affiliation.
More people are starting to agree with the academic consensus that theistic evolution is a pseudoscience and that there is no afterlife. These are sort of the last threads of refined, academic Christian philosophy, which has already been increasingly considering more and more of the Bible to be metaphorical.
Most of the educated Christians which remain tend to be pantheists, deists, and agnostics. Christianity has become more of a subculture than a religion for them, hence the term "Cultural Christians." As the Christian culture becomes more radical about its literal belief in an ongoing spiritual war, these non-believers are abandoning the mantle.
So I think you're right that the toxicity of modern Christian movements are driving people away from identifying as Christian, but I think it's important to keep in mind that this is rarely due to the toxicity causing people to question the coherency of their beliefs. More often, we're seeing marginal Christians silently distance themselves from a Christianity that has doubled-down on doctrines they don't believe in.
This has hardly any effect on radical strains of Christianity that promote, for instance, anti-intellectualism and fideism since they are predisposed against education.
That isn't to say that all remaining Christians are evangelical fundamentalists or anything, obviously. I just think there's a clear reason to the pattern of change we're seeing.