As a society, we need ways for people to get out aggression in a generally non-harmful way. Note that I'm not arguing against making football safer for players, but rather against the elimination of violent sport.
Maybe robo-football? There's just something fun about beating a consenting opponent to the ground.
Beeing a defensive end / outside linebacker I can say that the bigger positions don't really translate to flag football. You can't really block other people without real contact. We are playing 5 on 5 - but I can't imagine how contact less football would work 11 on 11.
I enjoy playing some flag football, because it's a nice workout and some of the aspects of football are in (different coverages, beating routes...)