I think the biggest factors in determing which sport you prefer is region and upbringing.
As much as I admire the athelticsm of socccer player, and I truly love national grudge matches like Brazil vs, Argentina etc...
I was raised by a father, who loved and coached American Football, and I was raised in a city during the dominant years of the Miami football franchises.
I have many latin american friends who love soccer because that it was they grew up loving. I have a good time with them watches their matches, but I will never love it as much as American football.
Its true football is violent, but there is also a complex side to it as DoJ eluded to with rules. I have coached youth football, there is an element to that makes it like a violent chess match, putting your players in place to either defend or attack your opponent. The rules are complicated, the only thing I can say the more you watch it, the more you pick up the rules. After while you just accept them as part of the strategy in the game.