Depends a lot on what we mean by "smart" and "benevolent."
For example, suppose by "smart" we mean not only intelligent, but intelligent enough to self-improve our intelligence in a for-practical-purposes-unbounded fashion. That seems at least roughly consistent with what we mean here by risky AI. And by "self-improve" here, we should include things like an agent building a system external to it, not just an agent modifying itself; that is, a system prohibited from editing its own source code but able to build another, smarter system and execute it should still count as self-improving for purposes of risk assessment.
And suppose that by "benevolent" we mean capable of consistently and reliably acting in the long-term best interests of humans.
Now, either (a) it's possible for humans to build a smart machine, or (b) it's not possible.
If (a), then humans are themselves a smart machine, so evolution is capable of building one. Whereas humans aren't benevolent, despite what would seem to be significant selection pressure for benevolence operating over the same time-period. That suggests that benevolence is a harder problem.
If (b), then this argument doesn't apply, and benevolence might be a harder or easier problem, or neither. That said, if (b), then it's not clear why we ought to worry about AI risk at all.
Humans are semi-benevolent. I believe that if people in general didn't do more good (behavior which leads towards human survival) than harm, the human race could not have existed as long as it has.
By observation, it's not a matter of a small minority of people who make things a lot better vs. a majority whose effect is neutral or negative. I'm reasonably sure most people do more good than harm. The good that people do for themselves is included in the calculation.
This doesn't mean people come anywhere near a theoretical maximum of benevolence. It just mean...
It's way late in my time zone and I suspect this question isn't technically coherent on the grounds that the right answer to "why care about AI risk?" is going to be complicated and have a bunch of parts that can't be separated from each other. But I'm going to share a thought I had anyway.
It seems to me like probably, the answer to the question of how to make AIs benevolent isn't vastly more complicated than the answer of how to make them smart. What's worrisome about our current situation, however, is that we're currently putting way more effort into making AIs smart than we are into making them benevolent.
Agree? Disagree? Have an orthogonal answers to the title question?