Of the very few "f*cks" I can give in my life, I prefer to spend mine as I choose rather than being scolded for not giving mine to the pressing issues that others deem important.
If you truly care about the planet, don't have children.
At the very least don't brag about not giving a crap.
That's a fallacy; people care about the planet precisely because of children. I don't care about the planet for its own sake; I care because of the humans who inhabit it and their future lives.
Also, humanity spent 100,000 years without flying around the globe, and I doubt they were all living hermit martyr lives.
The fact that I happen to care about other things more than this specific flavor of global catastrophe is morally OK.
I'm also not going to take shorter showers when people are farming in a desert and shipping the crops to China.
You might think this makes me a terrible person. That's probably good. Because it will help people understand what we're up against and what needs to happen to actually solve the problem.
"Take less flights" isn't the solution.