I also get rather irritated by mass collective nihilism of this kind. Human beings are a part of the natural order, so pretending we are somehow a plague on the planet is nuts. Yes, we need to be better stewards of our resources, but enough with the self-loathing crap.
Thanos was a very well-written, well-motivated villain. But he is a villain. I doubt these "Thanos was right" twits would think the same way if he snapped away their nearest and dearest.