I think there is some difference of degree, but not of kind. A determined terrorist can relatively easily find many ways to kill people en masse today, no AI needed. The bottleneck is usually the actual physical execution in the real world, not theoretical knowledge.
And the interest or willpower too. People fall into a kind of reductive Good vs Evil mode of thinking, with "terrorists" being of course a kind of shadowy mass of pure evil lurking in the darkness. But actual real life terrorists are people too and I'd wager few of them are actually interested in trying to end humanity.
Even the religious extremists don't really want to take over the world and destroy everyone who doesn't convert. That's just a way to gain support from a conservative nation. A lot of them are motivated by revenge for wars that destroyed their country and want to make sure it never happens again.
Their methods are wrong no doubt, and not very effective, but the reasons they do it are good. And a person like that will never release a deadly bio weapon. We should worry more about incel mass shooter types who believe everyone is evil.
If we are not careful and suddenly release tools with far more capabilities than we expect you go from "smart" people being able to do it, to some angsty teenager being able to pull it off in their bedroom.
The current issue with AI is we are squirting out new models faster than we can complete long term testing on them. We'll find new model capabilities long after they've been in the field. Just assuming safety is how you catch cancer from your food dye, or how you change the atmosphere around you and start burning down your planet. Now just imagine that involving intelligence and doing with a few percent of the worlds GDP to make it happen.
Plans for 3d printed weapons are publicly available, same argument was made then, if everyone can download a blueprint for a gun, are we all going to get gunned down? Hasn't happened. There's two errors in this Bill Gates argument. One is thinking terrorists don't already have PhDs, secondly overrating intelligence because that's the only thing they're good at, and when they think of terrorists they just think of their own inflated egos, but turned evil. Which isn't how real terrorists operate