What goes against that though, is that they were also trying to create more Nobodies.
Indeed, but from their point of view, being a nobody is not the absolute horror Sora see the situation as, and it makes more 'people' to their cause.
I am just disappointed by Sora's behavior. Did he really need to mock Demyx every time he saw him and to think only at destroying nobody? He didn't even once think to a way to help them to become whole without exterminating them.
Let's say, that those from Sora's side would have showed a little of
good will. Like, if DiZ was not obsessed by taking revenge on Xehanort, if Mickey had been more open minded and if Yen Sid had not been like "They're the incarnation of evil, never even listen to them!!"
Well, the ending could have been very different. I am not sure Xemnas would have easilly been convinced etc, but I don't think he'd have said no to negotiations, even though he's kind of power hungry he still want the 'good' for Nobody, he wouldn't have refused a peaceful discussion with the Keyblade wielder, but instead those took their keyblade and yelled "We're going to annihilate you!!!"
They have been totally rejected by others people and the worlds, I don't say the way they chosed is the good one, but it was the only one remaining to them considering how stubborn Sora & co were.