The pro/rel people have a good argument in that a team like Colorado or Philly just can't suck every year. If Colorado sucks every year and pays their players nothing - the only consequence is maybe the fans don't show up. They hopefully make a profit, collect merchandise and tv money and plan to do it all over next year.
If there was relegation, Colorado would have to invest in their team. Otherwise, the highlight of their season would be the visit of the Cosmos instead of this year when Villa, Kaka and Gerrard visited and they sold out the stadium. That's the argument.