well, the answer is this: read edmund burke, who actually called for the kind of "religious tolerance" that we associate with bourgeois liberalism, nowadays. but, then read marx and put it into perspective as to why.
this spectrum flip isn't unique, but it's endemic.
if burke was writing today, everybody would call him a liberal, and republicans would smear him as a socialist. but, he wouldn't be - he'd be the actual conservative, and the actual conservative position on religion is to be tolerant of it, so long as you pay your taxes and do what the queen says.