Roughing the Passer

Im sure this topic has been well discussed other places. I however dont visit other places nor do I watch many other teams. With that being said, the value of Dlinemen will probably dramatically diminish with these types of rules...attempting to sack a QB can be as much a liability as a boon.
Furthermore, are the rules even realistic? We see the replays in slow motion, but in live speed, these things happen so quickly that it would seem almost impossible for a Dlineman that has already committed to tackling the QB in hopes of a sack to stop his forward momentum. Its pretty soon DE's are going to be afraid to even try and get a sack.