Kane does not need to betray us, in this situation. He's getting everything he wanted, more or less, instead of losing and dying. Us losing and dying might appeal to a little ember of spite in his heart, but that's not much.
Kane also isn't against the human species, and never has been. He had options. He chose to live on preindustrial Earth for literally thousands of years in peace, enjoying the company of friends, lovers, and colleagues, in spite of certainly having continuous frustrations about human failings and the conditions of society around him. He was content to be an open hand of inquiry and progress instead of crash industrializing to spaceflight with an army of super-nerds and getting himself the hell out. This was after he got his soul ripped in half, too.
For all the disappointment of his time in the Soviet Union, he just dusted off his feet and left. We weren't ready. It was only tiberium. That's it, that's where Kane snaps. When that meteor fell, it placed him in an impossible situation, at a time when humanity seemed to be regressing during a critical point. He focused all of his traumatized intellect into solving that problem, and Nod arose from it. Even here in this negotiation he's laser-focused on his hopes and disappointments regarding humanity.