There isn't a Christian alive who gets perfectly right how Jesus wants us to be, and there are also a lot of Christians who get it not-even-close to right.
Besides, I didn't say "yell." There are lots of ways kids can and do quietly stand up for their beliefs in school. In this case, though, telling another kid the very construct of their family is sinful is justifiably going to feel like an attack,
I've been in education for over 27 years now. This kind of stuff happens a lot. Way more than outsiders know. And it IS complicated. I know the way I lean on this makes it easy to lose sight of my concern for pisgah's kids, for example, but I care about them, too. Handling things like this in a classroom is really difficult and you want everyone to come out okay, so a whole, whole bunch of thinking goes into it.
If I were talking to a structural engineer about something, I would expect their explanation or concern about a certain project to be more complicated than my take on it. Not overcomplicated, but appropriately complicated.