I support Brighton because my Dad does. I'd imagine if he support Man U then I'd support them.
EDIT: I guess club support is, or can be, a choice. The idea that I have to support the national team because I happen to be English doesn't truck with me.
Right!? Nothing like supporting a team just because you happened to be the one sperm that got through and, when you won the first race of your life, your parents happened to live within one set of borders and not another! WOO! GO ENGLAND GO!!