In the "everybody's kinda shit" argument, can't quite see the reason for ghettodians being considered that. They, much like the survey corps, seem pretty close to blameless.
I was even entertaining the argument that erwin might've been a bit of a shitty person, but... he was depicted as being quite fucking honest with his soldiers wrt what they were going to do, and why.
The average person in the ghettos or living within the walls has no "blame" because they're just part of the setting and have no active role in it. The Survey Corps are most comparable to the Eldion rebels who were actively working to topple the order. Now, we can argue that they are doing it with good intentions and want to change a broken system, sure, but their actions aren't always the most informed and they act out of passion and instinct rather than informed knowledge.
Look at how Eren's father "translated" the ancient documents to justify the rebellion. He admitted to not knowing what it really knows but inferred the meaning he wanted out of blind faith that their ancestors were innocent and that the ruling party has simply taught them lies to suppress them.
In the same way the Survey Corps have launched a coup and totally upset the order of things within the Walls, but even know they realize that they never really knew the truth behind some of the things they were involved in. They were interested in overthrowing the royal family who they saw as bad, to put someone in power who they could trust, so they could push forward with what they felt the people needed. Noble intentions, but I would hardly say it is innocent or blameless when there is actual bloodshed involved.
Ultimately, it is true that the core team of the Survey Corps are the most heroic and likeable part of the cast, but as the protagonists in a huge mainstream shounen action manga, they kind of have to be lol.