I was going to add, as a user of both Steam and YouTube, I have seen far worse stuff in YouTube comments than I ever have on a Steam forum.
I think part of this comes down to the fact that disgusting, hateful comments will pop up on almost any YouTube video in the comment section, but you actually have to navigate to Steam forums with this content.
So, YouTube comments are thrown in your face and hard to not see, as they are right below the video, but Steam forum comments are at least hidden behind a few layers of clicks.
I agree that singling out Steam as if it's the main problem, isn't going to fix anything, at all.
Nazism and promotion of terrorism are explicitly illegal in some places, while death threats are not explicitly illegal everywhere. So does your opinion on these flip flop depending on where you live?
How about grow a spine and get some morals of your own? Ones that are not dependent on whatever is legal where you are currently located.
If nazism and promotion of terrorism are fine with you, I don't think you are going to find very many friends here.