Thanks for all the interesting responses. I must say I enjoy watching football on TV but I very much dislike the general atmosphere in the stadiums. Granted I have not been to many big matches so I don't have much experience to draw from, but my few visits have been enough to really turn me off.
Last September for example I went to see the Champions Leage match between Marseille and Dortmund. I got the cheapest tickets, which was in the "Virage Nord", the most notorious part of the stadium apparently. But before and during the game you were mostly supposed to participate in insulting chants towards the fans of the other team. Usually calling them gay and so on. I have an aversion of chanting anything in large groups, let alone calling people gay which I assume is seen as an insult among these people. It was odd though because people were also impressed by the performances that the other fans did. But then they would go back to calling them gay and so on. Someone told me they were surprised that the fans of Dortmund got placed so closely to the Virage Nord, "if this was the fans of PSG, you would see all kinds of objects flying their way".
Most people were drunk or high, the general atmosphere was quite agressive. Luckily Marseille won 3-0 and there were no controversial decisions in the game, I wouldn't want to know how the atmosphere would have been in that case. After the goals people freak out and there is a giant moshpit, but since it's on ranks and not on flat ground it's freakishly dangerous. During one of these moshpits my friend got his nacklace ripped from his neck and almost got strangled. On the way home I saw the buses of the Dortmund fans, each one escorted by two police vans.
And I'd like to reiterate that this was a very uncontroversial game with half the stadium empty due to renovations and with a very good outcome for the home team. I think it's just sad to see that this kind of group mentality attracts so many people, even if all the group does is insult others, get drunk and do moshpits. If I had kids I wouldn't take them to a game, not even to the safe areas where there is seating, the general atmosphere is just way too hateful and agressive.
I have been to MLB, MLS and NFL games and the atmosphere is completely different. Baseball is completely peaceful and NFL and MLS are a little crazier and people are more drunk but still it all seems like one big party and not some kind of a war between fans. I feel like people really go there to see the sport and to celebrate the sport, rather than get their heads smashed in. Maybe it has to do with the very strict alcohol rules in the US or maybe also with the fact that not many fans can afford to fly across a continent just to see their team play. Maybe it also has to do with the fact that a lot of teams come and go quite quickly so there is no time for a fan "culture" (as they like to call it in Germany) to grow. But when I think about all the hate and violence the word "culture" seems grossly inappropriate!