There's a lot of hypocrisy around. The issue isn't pronouns, the issue is: Does a child have a right to keep secrets from their parents?
The ones saying "no" are probably keeping or kept a fair amount from their own parents. I mean, the ones who say "yes" probably did too, it's pretty universal, but they're not being hypocrites about it.
I wonder, if you changed this question to some other hypothetical secret, how would the responses change? What about... "Does a teacher have an obligation to report if a student is dating someone?" Or maybe, "Does a teacher have an obligation to report every book a student reads (on their own time) in case it's a book the parents don't like?"
I get it, too. I'm a parent. The idea that my kids might have secrets kind of bothers me. I want to be a part of their lives, I want to help them with any problem they have. But they have a right to their own lives, and the only way I could even try to prevent it would be immensely damaging to them in the long run. I can only do my best and hope they'll see that and be comfortable talking to me about the important stuff.