I see many keepers try pull out, but failing because of momentum.
If the keeper gets the ball first, he can take out the attacker afterwards to some degree (if the ball changes direction so that the attacker no longer can get to it). The penalty awarded to United was totally wrong. Gomes got the ball.
When running at high speed the slightest contact will put you off balance. The attacker has every right to go down. Especially when the ref never award the penalty if he stays on his feet.
I disagree that these injuries are part of the game. This is why attackers leave a leg behind. They make sure the feet is off the ground to avoid broken legs, but they still occupy the area which the keeper is about to enter. This looks like the attacker goes down early, and the attacker would look like a fool if the keeper actually manages to pull out.
Of course some injuries will happen, but the players must protect themselves. Jumping off the ground when a defender or the keeper clatters them is one way. I don't want to show videos of what happens if their feet is on the ground. There are horrendous leg breaks. And we have smaller injuries too. Remember Kane's small injury against Millwall? his foot was trapped between the ground and the defender. This is also one reason why the scissor tackles were outlawed. too many injuries.