It didn't take much. I never believed in gender ideology and didn't think that anyone else seriously did either. In high school I knew one trans-identified person, a gay man who went by a woman's name and put a lot of effort into looking feminine when he went out to clubs. No preferred pronouns, no discussion of queer theory, no using the women's restroom, no insistence even that he had been born in the wrong body, though perhaps he felt that way. That was pretty much the extent of my exposure to "trans" people until some fifteen years later when unhinged straight men started popping up on r/actuallesbians and talking about girldick and shit. I was never okay with that and when I spoke up, got banned, found my way to r/GenderCritical and learned the full horrific extent of what was going on, that was it for me.