I don't think this is the best way to proceed, as it burns bridges (and can also create a bad reputation). You should instead ask for a bit more time so you can make a fully conscious decision. 

If they don't give you this time, and in the end you “back out”, I don't think there will be a legal consequence, as you have no signed contract (and I assume no other signed document whasoever).

Companies usually don't bother to go to court, as you only know the contract content when you are about to sign it… and you have the right not to sign it. But on the other hand, you are going acting in good faith when you refuse the contract… Of course if they don't give you time to weight your options, they are not acting in good faith as well.

(edited)