Let me get this straight.
If you as a defender bump, turn, or facescreen a receiver, that's pass interference, and the ball is placed at the spot of the foul, even if that spot is 50 yards down the field.
But, if you come flying across the field and drill a receiver who is attempting to catch a ball in the head so hard that he drops the ball or completely misses the catch, that's a personal foul ("hit on a defenseless receiver"), penalized by 15 yards. The difference is the timing -- arriving at the same time as the ball instead of before. But the fact of the matter is, it's still a situation where a defender may choose to commit a penalty in order to stop a catch.
If you really care about player safety, then make the blow to the head a bigger penalty, and give the offense the ball at the spot of the foul. Otherwise, if the pass is longer than 15 yards, the defender still has an incentive to drill the receiver in the head and make him drop the ball. The defender is discouraged from just holding his hands in front of the receiver's face -- that's interference -- and instead encouraged to do something more dangerous.
I understand that they try and assess monetary fines to players after the fact, but that only bolsters the case. If you're going to fine someone tens of thousands of dollars for something, shouldn't it be worth more than 15 yards during the game??
And either way, the pass interference penalty should be reduced to 15 yards, like it used to be, because it's too arbitrary of a call to have that much weight, and I'm tired of watching QBs intentionally overthrow the receiver just to try and draw the call.