You could literally develop a hyper-intelligent advisor on how to kill people or perform dangerous hacks using ablated 'open source' AI. You can do this right now, this very moment, and have an extremely adept advisor on how to do really, really bad things.
So? The primary thing stopping people from doing really really bad things is, and always has been, most people not wanting to do bad things.
It's never been difficult. Literally, right this second, you could grab a pen off your desk and pretty easy ram it into the neck of your nearest coworker. Killing's easy. You don't need some hyperintellect to tell you how to do it.
The reason you haven't rammed a pen into your coworker's neck is the same reason why most possible really bad things don't happen: People don't want to do them.
I already know how to kill thousands of people. It's not conceptually difficult: more than a day's effort, sure, but what stops people from doing this kind of thing is not the lack of knowing how. https://xkcd.com/1958/
My level of trust in Anthropic/Google/OAI/Microsoft/Meta not to do bad things is about zero, so why should I trust them with this?