I don't want to get into a debate about nationalism in sport, since that could go on forever, but I feel like you're broad brushing US national team and MLS fans pretty hard there. USA fans have a well-founded reputation for traveling well and behaving themselves. It's the one area where I feel OK being patriotic without feeling like a bullying *******.
Yes, the USA is an international bully, and I find American patriotism nauseatingly excessive quite often, but, frankly, international football is the appropriate venue for flag-waving and patriotism (provided it is not done in the violent Balkan style). If the English can't be bothered that's fine, but it's not fair to compare your own ambivalence to our enthusiasm and deduce a "vicious" nationalism. I remember being at a USA-Mexico WCQ once and apart from a couple drunk idiots everyone managed to be very patriotic on both sides without it turning sour.
As for club football, there was a time when "Liverpool FC" consisted of one angry landlord. Were Liverpool's first fans in 1892 a bunch of plastic johnny-come-latelies, or were they legends, the vanguard of a storied, unimpeachable tradition of footballing excellence? (Or maybe just people who wanted to watch football and who lived near Anfield...) Just because MLS started things top-down doesn't mean the clubs have no history, no identity and no 'real' fans. The franchise system has also slowed the influence of money on competition.
Moreover, if you look at the history of football in the US, you will see a rich system of leagues and cup competitions in the 19th century, particularly in industrial towns. Our biggest cup competition, the Open Cup, dates from 1913 and is still running. The presence and popularity of baseball and, subsequently, gridiron football prevented that system from growing into a top professional league - but there is a very deep, rich history and tradition of football in this country that has never died out and feeds into current leagues.
Everything has a beginning, and despite the single-entity system MLS does have real fans, and that base is growing. When I lived in Ohio I used to drive 180 miles each way to see games, and I was not the only one. Columbus Crew has local sponsors, has fielded local players and is still a very affordable, intimate experience.
