Crowd violence is very rare indeed in English football these days. I can't recall the last time I witnessed a single incident at or near MCFC for eg, I dont include the moron who threw a coin at the recent derby. The nutters who want to fight do it far away from the stadium, if it happens at all. There are very few cases of group football-related violence prosecuted in courts these days. Many families go to watch live football on a regular basis.
Football can be an exciting and entertaining game. I never played it after school and was no good at it then but it sets even my pulse racing at its best. This raises emotions and there is historical competitiveness between particular teams. There were over 47000 fans at the Liverpool-v-City game last weekend and not one incident of violence inside or outside the ground as far as I know.
Finally, it is a great leveller between people, I have lost count of the number of times I have travelled abroad and struck up a rapport with strangers, who often barely spoke English and I nothing of their language, purely based on football.