Don't know how long this thread will stay open as this topic tends to get locked (pun intended... ), but detractors typically fall into 3 camps: 1) Don't like the aesthetics; 2) Don't like the political inspiration for the lock; and 3) Don't like that the lock can cause the gun to freeze up, potentially in a life-and-death situation.

There's also overlap among these groups.

There've been multiple threads on this topic, so I'd suggest doing a search. There's also a sticky posted at the top of the Concealed Carry subforum by Massad Ayoob.