When does doing unsustainable things for mental health cross the line?

I've seen many people here say doing things such as eating plastic wrapped convenience food, taking long showers, even travelling long distance, is okay because it helps you mentally. But where is the line drawn? I'm not trying to attack anyone, I'm genuinely just wondering at what point the individual matters more than the greater good. If I said flying around in my private jet improves my mental health, I'd be a selfish asshole. If I say driving cross country does the same, it's okay? What's the line? Is it a certain amount of carbon emitted? Genuine question.