Because, eventually, the "student" moves beyond our care with his own opinions. And, at that point, it's probably harder to tell ourselves that he might become something different when he has already become something.
But I don't think that we can endorse something that we don't believe in. At least, I don't think I could. Maybe I could congratulate my former student on his latest endeavor, offer to talk through his positions with him and be a sounding board, maybe challenge his positions or let him know that I don't agree with what he's doing, maybe even go so far as to make a nominal contribution.
Ultimately, I think that, in that position, we do our best with love and support, and that he knows that we offer love and support without agreement, not that we wholeheartedly jump onto a bandwagon when we don't want to take the ride. After all, Obi-Wan reminds us, through his actions, that we only enter into battle with a former student reluctantly, when there is no other option. But we have to confront him, don't we?
Sufjan's latest has nothing to do with my post. He's just so damn good.