A central planning AI to impose fairness and the right to basic survival could only come about and remain standing if there was enough support for it from those already in power to allow this. How would you suppose this would come about?

The future will hold a very different scenario than a typical first-world country today where the populous actually produces useful work. As a leader, instead you have a population who who in-fight amongst themselves for the best of the consumable goods and produce absolutely nothing of value for you. To make matters worse, they continually attempt to push their boundaries, growing bigger and bigger if not thwarted (as life normally does).

My other point, that techno-baron A will want to fight/defend himself against techno-baron B still applies. Won't anything that techno-baron A needs to do to defend himself against techno-baron B trump the humanitarian concerns for maintaining the lifestyle of his subjects that give absolutely nothing back to him?

Even if techno-baron A is morally inclined to do so, there will be others that are more brutal and would not. And even if the moral techo-baron A is able to completely conquer the world (seems very unlikely considering how schizophrenically both brutal and compassionate he would have to be), then his hold on it will at some time cease, probably under duress from threat(s) within.