There definitely seems to be an increasing problem in violent and anti social acts in public now, not just in sport but in many other walks of life. It is borne out in statistics that common assaults have been rising since around 2015, and gone up sharply in the last couple of years (I saw a graph the other day but cannot for the life of me remember where).
My theory? The proliferation of social media in our lives, and the increased polarisation of the population because of it. When people can only see opinions in 240 characters all nuance is getting lost, the art of debate and respecting others' opinions/loyalties is dying, and being abusive to each other online is becoming so normalised that it is now seeping into face to face encounters. Football is starting to show this quite starkly, given it is already quite a powder keg environment, but it definitely is becoming a problem elsewhere too.
However, there are honourable exceptions still. it was heartening to see in the Europa League final, despite 100,000+ Rangers fans travelling and I think around 60,000+ Frankfurt fans, there was only one arrest (a German fan).