like mentioned, the phoenix force didnt change the people it possessed or forced them to do things against their will. it amplified their desires. thats why piotr tried to get kitty back. i dont see how they get praised for all the humanitarian stuff they did while possessed, but when namor took atlanteans to war to flood wakanda, it was the phoenix doing
But that's the thing. It amplifies our desires, good and bad. When you want to do good and you can do it the choice is pretty simple, like the P5 doing humanitarian stuff.
On the other hand people want to do bad shit all the time, but usually we manage to refrain ourselves. How many times have you wanted to punch someone in the face but you didn't do it? How many times did you wish you could kill some motherfucker who did you wrong but you didn't actually do it?
Colossus wouldn't normally do what he did to spidey but the phoenix made him lose control.
Cyke wouldn't kill Chuck even if sometimes he consciously or unconsciously wished to, but the phoenix made him lose control.
Namor wouldn't normally destroy an outside country and kill innocents just to capture a bunch of guys, but the phoenix made him lose control.
The story is pretty clear that these guys were not in control and where not their usual selves. Even the X-men who supported then in the beginning realized that and abandoned then.
You say people give a pass to the P5 for doing humanitarian stuff and is easy to see why. Doing good is in their nature, it's usually what they do. Attacking or killing friends and innocent people is not.
And a lot of the guys saying it was OK to destroy Atlantis and commit genocide were the same guys saying Cyclops should get a pass. If Cykes gets a pass so does Namor but mostly so does the Atlanteans who were just doing what they were told.
Namor's judgement was not only corrupted by the Phoenix, but he was influenced by Emma Frost. She made him do it. Without her influence Namor probably wouldn't do it.
Now, everything I said don't makes Namor innocent, and he certainly has to pay for what he did (I don't think BP wanting to get revenge is wrong or out of character) but I think this is enough to show how Shuri was wrong in attacking Atlantis like that. Even T'challa thought it was wrong, he wanted to make Namor pay, and no one else.
I may be wrong (and someone correct me if I am, I don't read many X-men comics anymore), but to this day I haven't seen Cyclops acknowledging what he did. He stills maintains he was not in control.
He did own up to it the same way Namor said he was going to own up to saving the universe a couple times by destroying alternate Earths with the Cabal.
In the end I'm just happy this story is so great that it generates such heated debates. Hickman is good.