I go at it from a slightly different angle.
I'm not a fan of any form of childhood ideological indoctrination (whether it be liberal or conservative leaning, or whether it be religious or secular leaning)
Not necessarily because I think it's particularly bad for someone to want to promulgate their own values, I think everyone has that urge to make other people see it their way to some degree or another, but because I think it's highlights an insecurity.
That's not to say that people can't be persuaded to convert to/desist from any ideology when they're adults (there's people who engage in faith and ideology switching in their 30's and beyond).
But if the core strategy is "hook 'em while they're young and impressionable, so that they'll go along with everything I say because they see me as an authority figure and by the time they're older it'll be so ingrained in their mind, that they'll stick with it", operating on the premise of hoping that Aristotle was right about the "give me a child when they're 7, and I'll show you what they'll be like as an adult" theory, I think that's a short-sighted approach and one that projects a certain weakness or lack of confidence in one's own ability to make a strong case for their viewpoint.
Someone who's easy to convince is also going to be someone who's easy to "unconvince".
Perhaps it's just the phrasing, and maybe you didn't intend for it to come across that way, but referring to it as "the schools undoing what I did" comes across less like a sincere desire for intellectual honesty and a marketplace of ideas, and more like something someone would say if they were disgruntled because someone else's brainwashing over another person supplanted their own.
Abridged version:
Good ideas should be able to win over adults who've reached the age of reason without having to depend on "getting to them while they're young", and good ideas shouldn't require one to prevent the person from hearing all other ideas that may conflict. As soon as someone says "well, they shouldn't be able to tell them XYZ because if they hear that, then they may not agree with me anymore", they've already conceded a large chunk of the debate.