They are saying that the actual victims, the folks in the towers, did not deserve to die. Everyone agrees that the attacks on 9/11 were horrendous. But the US had engaged in activities where this was the inevitable outcome. America as an entity deserved the attacks because of decades of wars, conflict, and instability it caused in the middle east, often leading to similar if not greater acts of violence in those countries. This isn't a fucked up sense of justice, but an acknowledgement that at some point the roosters were going to come home to roost.

USA as entity deserves hate of the world, and hate radicalizes people into becoming "psychopaths". Acknowledging the fact that USA created opportunity for 9/11 to happen doesn't mean it was good that it did. Even now, when USA is waging this senseless war with Iran and people see their families murdered for no other reason than Trump wanting to steal some money, that is creating more people so full of hatred and frustration, that they will see violence against anyone they associate with their enemy as justified. I'm not (and neither is anyone speaking of blowback) saying that the cycle of violence is good or justified, but recognizing that USA starting it and continuing to escalate it LEADS to the potential blowback is necessary. Furthermore, nobody is saying that Al-Quaida or Osama bin Laden bere justified in planning and executing 9/11. And I'll even go as far as to say that they might have done that sooner or later regardless of USA murder spree in middle east, though it would be completely different timeline and very unlikely. They didn't do that in vacuum, however. They had all the reasons (and don't forget about training and weapons they received from USA) to hate, to be radicalized the way they were, to go crazy from the suffering that was inflicted on them. Do you understand now? Nobody is saying that 9/11 was good, or that Al-Quaida was good, or that the victims deserved to die. America deserved a blowback for what it did in middle east. It created support for those ideas in the minds of people who lost everything because of USA. The more hatred it caused, the more likely a blowback became. Only reason I say "deserve" is not the perfect word to explain it, is because the way it is usually used suggests some sort of justice being served, invokes emotions of satisfaction with someone bad getting punished and so forth. However, you claiming that "america deserved 9/11" means the same thing as "people who died in 9/11 deserved it" is just sophistry on your side. You know they aren't the same statement. And if you didn't, well, now you do. Stop being obstinate.

That we can feel superior to all parties by pointing out the obvious?

That had we not had a history of committing acts of of mass violence in other countries, we wouldn't have deserved to have one committed upon us. We did though, so we do.