Now you're getting into the territory of forcing already overused bullpens to have to pitch more innings.
The game is different now, bullpens are used extensively guys are throwing harder, the rules of the game have to change. Mercy rules have existed in baseball at various levels and various tournaments. It's nothing new. The whole fans paid for the game stuff is irrelevant because most fans don't really care once the game gets to this point.
Maybe don't allow it until at least the end of the 7th, but teams should have the right at that point to say, we're beat, see you tomorrow.