The thing that stands out to me in the whole situation is the fact that... Just listen to Joker's delivery. He KNOWS he's saying something tasteless. But the jokes have ALWAYS been his coping mechanism. So he just watched a planet burn, he knows that his CO was down there and couldn't stop it from happening, and his father and sister are missing without any word. He NEEDS to do something to cope with all of that, and that's making jokes. And he clearly knows that it's WAY too soon for there to be any humor there, but can't quite help himself. I generally play my Shepards as having a similar sense of humor, of utilizing jokes to deal with whatever they're going through, so, even though they'd think it was in poor taste, they wouldn't tear him a new one for that. Maybe a 'I hope you aren't going to repeat that to Liara, otherwise I'll end up needing a new pilot,' but not the overreaction that there is.
But the galling thing for me about Thessia is how the Reapers are already there when the Normandy arrives. Thessia falling was a given - the length of the Reaper's occupation would be up in the air, but the Reapers had Thessia, and that's all there was to it. There was no way to just boot them off - even if they did get the Catalyst then and there, they'd still have to take it to the Crucible and get it installed. So Thessia would still have been occupied by the Reapers. Then, when Shepard GETS to Vendetta, it takes... what is it, four times for Vendetta to actually answer Shepard about the Catalyst and agree to give up any information about it, instead answering everyone else's questions and basically saying that 'nope, the Reapers are already here, you're doomed, I'm out.'
So, let's look over our list of who is responsible for Thessia falling and the loss of the data from the beacon, in no particular order:
The Reapers for invading in the first place.
Vendetta for backtalking Shepard when he could be giving up the vital information.
The protheans for designing Vendetta to be so obtuse and quick to give up on the 'primitives'.
The matriarchs for hiding this vital piece of technology that could change the course of the war until the eleventh hour.
Kai Leng/Cerberus for showing up when they did.
In the list of responsible parties, Shepard doesn't even rate the top five. Yet regardless, we ALL get a Shepard who blames themselves ("Thessia's fallen and that's on me.") for it, and is openly depressed about it. And it bugs me because as bad as it is to watch a world burn, my Shepards have no connection to Thessia, no reason to take on the blame for what happened to it themselves. Planets have been falling to the Reapers left and right at this point, if Shepard took each of them as a personal failing, there'd be no way that s/he'd be able to function. The loss of Thessia, yes, is sad. But the exact same damn thing is happening across the galaxy. Why does Thessia get Shepard depressed and broken instead of, say Terra Nova, or Palaven, or EARTH?