> but it's clearly irrational to make sacrifices, when other people are unwilling to do that.

You realize that if everyone has that attitude then nothing will ever change, right? "You take the first step!" "No, you take the first step!"

> Why should the average person reduce his/her life quality in order to save the climate, when the average billionaire

I understand (and share) the sentiment, but there are not that many billionaires. Even if they all suddenly became vegans who never travel and live in a small house, that would not solve the problem. What the masses do is what has to change. How they travel, what they eat and buy and consume, their housing.