I don't know about the god thing you mention and the rationalist stuff I've read hasn't been about that. The main argument as I understand it is:
1. AGI is possible
2. Given AGI is possible if it's created without the ability to align its goals to human goals we will lose control of it.
3. If we lose control of it, it will have unknown outcomes which are more likely to be bad than benign or good.
Therefore we should try and figure out a way to make it safe before AGI exists.
Maybe humans just happen to be an intelligence upper bound and anything operating at a higher level goes crazy? That seems unlikely to me given that humans have a lot of biological constraints (heads have to fit out of birth canals, have to be able to run on energy from food, selective pressure for other things besides just intelligence). You could be right, but I'd bet on the other side.
The last bit is if we can solve this in a way that aligns the goals with human goals (open question since humans themselves are not really aligned) we could solve most problems we need to solve.