And that, in and of itself, would be a good reason to oppose it. Basically, the compact says that in the event the popular and electoral vote winners are not the same, the election will be decided by the Supreme Court. Can any reasonable person think that's a good idea? Bush already gets chided for being "selected not elected" despite the absense of any basis for Gore to be declared the winner. Having the Supreme Court have to decide an unclear case would likely cause civil war.
I suspect it will be challenged well before the election takes place.