I don't disagree with your point overall, but there do seem to be plenty of kids that grow up despising their conservative parents' positions on politics. The question of whether they even want to spend time with their conservative family even implies this.

It's also possible that they will be the last person they'd listen to, since conservative families can have a lot of contempt for each other and care more about the hierarchy than who is right.

But that said, I fully agree that just cutting off people for being awful ends to driving them into the arms of other awful people. And if there's a lot of it, it can do things like get Trump elected because they are tired of being treated like the bad guys but get galvanized instead of discouraged.

It's also the goal of the divide and conquer strategy the ruling class is using to make us easier to manage.