Jack Dorsey would like to ‘delete all IP law’.

I figure that since proprietary software developers use copyright to stop us from sharing, we cooperators can use copyright to give other cooperators an advantage of their own: they can use our code.

Yes but the spirit of FOSS is clearly anti-copyright and a non copyright world would be preferable.

You don’t get to just do whatever you please with someones work.

The FOSS positions is that you should if you are not preventing that someone doing what he wants as well (or anybody else), which is the case with IP unlike real property.

It's also how the world has worked for millennia, copyright and other IP law is relatively new phenomenon and even in the time it has existed it has not been as well enforced or accepted by society as say the concept of physical property.

AI is a great chance for commercial interests to push pro-copyright positions with a narrative of big bad tech corpos (absolutely true) vs little artist guy (bullshit, it's big bad media corpos). I remember they tried to portray copyright and associated enforcement tooling (DMCA etc) as a solution to revenge porn, to rehabilitate it's image.

Also doesn't the GPL use IP law for enforcement of copy left?

That's very probably Jack Dorsey's motive in this. Briefly void all IP law, then restore it in a messy way that leaves everything owned by his lawyers.