At least you could rely on guys that weren't declaring for professional leagues to stick around for a couple years more. Now every year you might have a completely different team, so that might alter how players are developed and how coaches can coach. I think it is ultimately bad for the players and the fans. Sure the students might be getting a lot of money, but that doesn't mean they'll be developing into great players or have great NFL careers.
I see even among the elite program's players being moved around because one school might need a position player a lot more badly than another thus want to pay them more or vise versa.