I heard someone use the analogy of "If Magnus Carlson played me at chess, I wouldn't be able to predict the moves he'd play since if I could I'd be at his level. He'll consider things I didn't and even though I don't know the route he'll take to win, I can be certain he will beat me." (not an exact quote).

We're not going to be smarter than a superintelligent AI. The things we conceive it doing if it were given a malicious task (bioterrorism, killer nano-machines, pure fusion bombs sidesteping the non-proliferation bottleneck of Pu239, etc) are likely not the full set of things it can do to harm us. I don't think it does us any favors to dismiss the risks here.

Even the things we can conceive of are very scary, to me at least.

How do you envision a chatbot doing any of those things? You can't just program a super virus, nanobots, bombs etc. These things have to be created in the real world, you can't do it without involving a lot of humans using expensive tools and materials etc.

So to me it seems like the prime candidates to come up with stuff like this are researchers working in defense and similar fields, probably not some deranged lunatic in a basement. And certainly not a rogue AI on its own.