I'm not entirely sure what the complaint against expansion would be, beyond the obvious 'if you are questionably the 64th best team, you have no rightful claim arguing for a chance to be no.1'. That is, however, a really good complaint.
But given the constant talk and griping about teams that just didn't make it, or were screwed or whatever, it seems like the difference between the 55th best team and the 70th best team is a difficult one to make with anything close to objectivity. Plus from a viewing standpoint I doubt it would really bother people to watch st. mary's vs auburn in a play-in-type game over, say, whatever was on last night.
Meaning I get the argument FOR expansion, though I don't necessarily agree with it.