I totally agree with Kobe here. If you've ever played basketball, you would know that landing on someone's foot after shooting a J is not good. It happened to Pierce last year, I believe, and he sprained his ankle pretty bad. It screwed with Joe Johnson, Deron, lots of players. If you jump straight up and someone sticks a leg under your foot, you obviously can't see/avoid it. If you land on it, you twist your leg and crumple down to the ground.
Shooters and offense should definitely get the advantage in this case because they shot the jump shot. It's the defender's responsibility not to foul the shooter after the shot has left his hand. Sticking your foot under someone else is cheap and dangerous for NBA players, college players, even me.
So yep. It should not be legal for a defender to stick their foot under the opponent's leg while the opponent shoots a jump shot. Too dangerous.