You can’t blame De Gea for missing the penalty, there is always going to be a villain in a shootout. I’m surprised it got to 10-10. Maybe the only thing you can criticise De Gea for is he could have saved one?
I also don't think De Gea should be blamed for that. Goalkeepers shouldn't take penalties at all, in my opinion, only if they have talent for it. I'm surprised that no outfield player took the responsibility and scored a second time.