Overreactions here as usual. Obviously at fault for the third goal, but to be honest better that happened in this game than in any later games this season as this was already lost.
First goal, sure you could blame de Gea for passing Maguire but he asked for the ball and should be able to turn into space there. Much more on Maguire than on de Gea - especially if one think we should be a team playing out from the back. The second goal was unfortunate, could have saved it but hardly a mistake. Not a good game from him, but hardly the disaster that some people here are making out.
The second part is certainly on Maguire, but stating that doesn't mean De Gea didn't feck up horrendously in the first instance, so I wouldn't say it's on one more than the other. Nor is playing out from the back a defence, because playing out from the back still relies on the sense of the backline to pick an option. It's a playing philosophy not dogma, no team plays every single pass short or always to the centre back so I don't think you can just say "well we play out from the back, so there you go, deal with it."
Surely as a keeper you know your man. You train with him all week, you know he's not a first teamer or brimming with confidence. You know where all your defenders want the ball, to what side, you know their overall skill on the ball so goalkeepers are always aware of what the options are and it's something they should be actively thinking about. If they're not then what else are they thinking about in terms of on the ball play?
Then there's the in game factors. You can see a bouncing stadium in front of you, you know it is the early stages and the press is set and the opposition have energy, you can see the picture of where the Sevilla players are right in front of your face regardless of who is asking for the ball. Would DeGea also jump in front of a bus if somebody ushered him to?
All this stuff should be intuitive for a keeper at this level. It's ultimately a split second decision but that's goalkeeping, most of your job relies on a quick decision or reaction and the consequences are big.
I don't think there is any mitigation for DeGea. He takes full culpability for that bad choice. Then Maguire has to take full culpability for the fact that once that pass is played, a player at this level should be able to deal with it better even if he shouldn't have been put in that situation. Again it's about reacting to the situation and dealing with it, which he didn't.