Basically, while the vast majority of fans of both terms don't use them derogatorily, they also use them unthinkingly. The clearest proof that it's a bad idea is that very few Jews would call themselves yids, and very few American Indians would call themselves Redskins. I'm against mimsiness, but this just seems pretty clear to me. The Washington team name will change soon enough - lots of media outlets in the USA have decided not to use the word to describe them. And this should too.
Tottenham fans are subjected to hideous anti-semitic chants, they say. While that's nasty, it is worth remembering that most of them aren't jewish. Is there another way to respond than by proudly self-proclaiming themselves yids? (Remembering that they wouldn't self-proclaim as niggers, because that would obviously be offensive and people don't like other people thinking they're racist.)
I literally have an answer that I think might work. When fans of Chelsea or Man Utd or whoever it is start doing the awful things they do - which includes hissing in mimicry of gas chambers - chant back loudly, and in unison, and over and over again: Chelsea are racists, Chelsea are racists, Chelsea are racists.
People hate being called racists.