If you have an obligation to speak up, your obligation surely is to speak effectively. So if you're trying to convince children who are hearing from others that being gay is a choice and an immoral one at that, this analogy is unlikely to do anything.

This is my point: it's an analogy that only works if you already agree with its conclusion. If you're trying to convince kids at risk of being turned into bigots, you're better off just exposing them to positive representation and positive talk. Getting there via an argument that only works if they don't believe the bigotry is ineffective - or at least, it's no more effective than just saying "being gay is OK," while being less direct. And a smart kid who is hearing "being gay is an immoral choice" will realise that this analogy doesn't contradict what they heard from their dad or their friend and may become harder to convince due to having heard a shit argument.