Why not just train an AI to care about humanity then? One problem is in defining actually what it means to care about or preserve humanity. Another problem is creating an AI that actually internalizes this as a goal, instead of just saying the things we want to hear until it gains enough power that we are not a factor in its plans anymore.
It's probably possible to align an AI, it's just not a problem we've solved yet. We've seen many, many, ways in which things can go wrong with less-intelligent AIs, and there's no reason to think that things will just magically somehow be easier as the AI gets more intelligent.
An AI we train to take care of us will almost certainly learn to want some other stuff, in addition to not exactly caring about us the way we want. That's fine if it's not too smart, we just stop it from doing dangerous stuff. The problem is when you crank it up to a million, and then those things that are just a tiny bit wrong become a massive problem, and you can't turn off the AI because it is smart enough to understand that the things it wants to do won't get done if it's off, and it doesn't want to let itself be modified in the same way that you wouldn't want someone to give you a pill that makes you stop caring about your children.
And the first step to prevent that from happening is for us to stop, and then hope that the other powerful countries will see that and stop as well. And everyone who's left can be forced to stop by the powerful countries who agreed to the treaty.
The faint hope is that people are not crazy or suicidal enough to build a world-ending technology, that humanity will manage to see ourselves as being in the same boat, where we all live or all die as one. And just-not-do the thing that causes our extinction.
It's not a very realistic proposition, because even smart people often fail to understand these arguments (or just disagree with them), let alone the politicians (who are incentivized to ignore them), or the rest of the people. There's a lot at stake for the "winner" of the AGI race, who could build an AGI and align it successfully (which they can't do). And many countries are ruled by people who are clearly willing to do crazy and suicidal things for power.
That's why the author of this post doesn't put a lot of hope into the idea of his daughter growing up.
I also don't think it's that likely that a leader would take those odds, if they understand the risk fully. The worry is that they won't understand or believe the risk, so that's where we should attack the problem, in my opinion--by putting out as much good information on AI risk, and combating misinformation, as best we can.