Any group of people is going to contain a spectrum of intelligence, personality, aggression etc. They are no different, nor are we. Not all Leeds fans are violent, racist scum and not all Norwich or Swindon fans are inbred village idiots.
This Sunderland thing is a bit weird though. I was at the game in 77/78 and all the huge fuss about it seems only to have come about in the last couple of years. Coincides with their decline I think. When they were doing well they didn’t care, now they’re looking for someone to be bitter towards. Given that it was 40 years ago most of the ones banging on about it either weren’t born or must have been infant prodigies to recall it. And they’d have done the same!