Usually the issue is LGBTphobic parents convinced themselves anything remotely LGBTQIA is sexual in nature, and they must protect their kids, that if they actually believe it, and not just either “noble lying” (seen some christian fundamentalists admitting “it’s not actually harmful, but what if it’ll be too late for heaven?”), or just doing it for cruelty reasons (bigots, just like bullies, like to paint their targets as people deserving of the bad treatment).
And this also has a hidden assumption that talking to your kids about anything sexual isn’t good. That mindset can lead to teenage pregnancy because, like it or not, our bodies are wired to make sexuality easily discoverable, even if society wasn’t full of it (and it would still be full of it even if lgbt-ness could be dialed to 0).
On another note, wanting to suppress sexuality so that women have fewer options and might be more likely to choose those suppressing it is such a pathetic mindset.
