Oh, don't get me wrong, I don't want Goku anymore than you do solely because of those reasons. However I do think that the theory of them all dying and him wishing them back is just crazy enough to actually be real at this point. I don't want him in, however I can see some validity to the whole idea.
I don't agree with the idea of Sora doing the same thing tho. Sora originated in a video game, as did most of the villains and some of the supporting cast. Disney characters, on top of being owned by a ruthless corporation that doesn't want their characters to be shown in a negative light/losing (see MvC: Infinite), originated in cartoons. Does Sora being in the game open up the gate to other Kingdom Hearts characters? Yes, but only those exclusively made for Kingdom Hearts. Hell the dude has also been on a Nintendo console at some point before all this so he doesn't really have a lot going against him. Sora may not be high on my priority list for getting in, but he has just as good of a chance to get in as other characters. I still don't think that him getting in will pave a path for the likes of Donald, Goofy, etc. getting in.