Cancer is an exceptionally powerful analogy. The best I've yet to come across.
Tools like AI won't save or improve the world, as it has never been the original goal. If it was, then, as one of the commenters above pointed out, we would've done it with the technologies/systems we already had.
AI's goal to save the world is no more than the cancer cell's goal to save the host organism (it is not in its capacity to think that far, nor has it been in ours so far either). The goal is to maximize local gain, efficiency, power, and control.
AI is yet another tool to make status quo more efficient. The problem is not AI; the problem is status quo. Thus, its cardinal applications will lean exceedingly toward militarization, state control, social engineering, propaganda, corporatism, hyperconsumerism, and further colonization of human and natural communities. AI just makes this so much more efficient. The result is predictable; this is how complex systems collapse. It will be fortunate if the collapse occurs before the technology is powerful enough to sustain the system semi-permanently, rendering any immune resistance ineffective until the host environment is eventually terminated.
I think the future, if we are to have one, is not AI (or any other post-human substitute). The future is human. AI is a good indicator of the greater existential crisis that we are facing. Let's face it, we are fundamentally uncomfortable with being human. So it is a good wake-up kick in the butt for us.
[P.S. I noticed an interesting trend on H.N.: the most poignant and thought-provoking comments are constantly downvoted and flagged. It may be a symptom of the echo chambers that have developed here. I wonder if some API could be developed to save those comments, as, with some exceptions, I find them most interesting and useful.]