There actually was a case in Western Maryland in the late 70s where several cops were killed in a no-knock raid and that really did put a stop to the shit for a long time afterwards, but we need to end the war on drugs and we need to outlaw no-knock raids.
Certainly, there is no place for no-knock raids in drug investigations. Just knock on the door, and if somebody inside has drugs and flushes them then he's been punished enough with the equivalent of a huge fine (if he's part of a drug distribution network, he'll be in a lot more trouble for not being able to come up with their cut of the money he was supposed to make selling the now-flushed stash).