FIFA's rules hurt the US because of the upper limit on the number of teams allowed in a league.
......
I also don't know why you keep insisting this is a North American league, Mexican clubs have absolutely no interest in joining. This is still an American league with some Canadians trying to me-too their way in like any other younger brother.
You're going to hate me saying this, but TFC saved this league. I don't want to make this a US vs. Canada thing (because it's not Canada it's Toronto), but without the addition of TFC 3 years ago this league would be in a downward spiral. Next year after Phily joins it'll be hard to make the same claim (at this point we'll have 3 top-notch organizations in Toronto, Seattle, and Philly), but Toronto essentially showed the league what they were doing wrong.
Look at expansion since 2000 (3 teams in 7 years); Chivas in 2005, Houston in 2006, Toronto in 2007. Look at expansion since Toronto's success (4+1 in 4 years): Seattle, Philly, Portland, Vancouver, and in all likely hood Montreal. Look at WHERE these teams are placed; each creates an instant rivalry and most are placed in 'proper' markets with good existing support (not a single expansion team after 2007 is expected to struggle financially either). Efforts by each front office have mimicked and improved (respect where it's due) on TFC's efforts in the first couple years. Geographic proximity of the stadium to the 'central core' of each city has shrunk, and interaction with supporters groups has been ramped up exponentially (look at the shit Red Bulls/Chicago/Dallas fans have to go through) ... because of Toronto.
In addition to this, the supporters groups for TFC in themselves are top-notch organizations, and have join the existing groups (Barra Brava, Section 8, ...) and have pushed for changes in the league that will benefit US Soccer. This includes adding our support to Barra Brava for a downtown stadium, adding our voices to complaints against FC Dallas's FO for treatment of supporters, and trying to improve the CBA so we don't have players making minimum wage. In addition to this, the Canadian supporters groups (TFC/Impact/Whitecaps) are starting to put pressure on other Canadian markets to join lower USL leagues; I think there's even an idea to buy a USL PDL team in and around the Greater Toronto Area (ala Ebbsfield United).
I'm not trying to say that Toronto is the best MLS organization, we're the best team, we have the best fans, or any shit like that (personally I do believe this, but I'm obviously biased). But we do have a beneficial situation here (both to the US and Canada), and arguing against something that has given direct benefit to US Soccer is asinine.
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To knock off some of your points:
1) The South-East has had 2 teams, and Miami was supposed to be a 'sure-thing' expansion team with Barcelona as a partner. All crashed and burned horribly. The South-East is not ready for MLS.
2) Toronto Lynx (USL team) was horribly supported, no one can argue that. The biggest different between TFC and the Lynx is the age of the target market. 50% of TFC fans (in the stands) are men in the 20-30 age range; 5 years ago (right before the Lynx went USL PDL) this demographic wouldn't be spending money (even on TFC). They've successfully captured the 'baby-boom-echo' generation of sons (and some daughters) of immigrants, and timed the introduction of the MLS franchise perfectly.
3) Like everybody else is (for some fucking reason), you're underestimating the support for TFC (when claiming 'the passion won't last'). Our lasting support will be our third gift to the league
(the rivalry with Montreal will be the second; have fun touching each other's nuts Seattle and Portland!). It honestly hasn't even started.
4) Relegation (after a pyramid is created using USL branches and Canadian and Puerto Rico leagues) will benefit everyone, and will ultimately reward teams such as Toronto and Seattle because of their large fan base (the salary cap would have to be drastically changed, and in doing so you allow something equivalent to the 'big-two/three/four' that you see in European leagues). I want relegation, and I understand that if it did exist Toronto would probably be in a lower league right now. This does not bug me at all; I support Toronto till the day I die.