Did you even see the incident? You're acting like nobody actually touched him. Fred quite clearly stands straight on the back of his achilles heel.
Who are you to judge how much it should hurt and whether he's ok to continue. It's just bonkers to even try and pretend that he should have zero pain and iron tendons.
It wasn't a dive or pretending to be hit.
Like many here have said does it hurt? Sure. Does it hurt enough for De Gea to totally abandon the play, get to the floor and turn his back? No I don't think so.
It's clear he could continue playing, as the goal was given he sprint onto the ref didn't seem hurt there.
Im not saying he was faking a hit, but he was clearly exaggerating it.
I for one like way more the physical players that play through pain warriors such as Keane, Gattuso, Vidic rather the primadonas like Neymar that with the slightest contact they go down and roll over as if they got their leg broken 34 times per game.
If you have ever played football you know the pain when you get kicked or stepped on and while it hurts it's totally manageable, but for some reason professional players get away with exaggerating those and it seems that's ok with the refs and the fans.
I'm glad De Gea got punished, I'm sure if the situation happens again he won't act the same.