The purpose of a tool is important.

Guns have no other purpose than doing harm.

E.g. We don't blame cars, the tool, for driving into a gathering of people that can kill a dozen of them, we blame the driver. The purpose is transport, the same way LLMs for coding are a tool for assisting coding tasks.

We do actually keep cars out of areas whit lots of people here. And the media headlines always refer to a "car" driving into people. Whether that's the better than addressing the root issue is another question though.

We also don't allow car use without a license.

In the end what matters if allowing something is a net positive or not. Of course you can have more precise rules than just a blanket ban but when deciding and enforcing those rules is not free that also needs to be considered in the cost benefit analysis. Unless you can propose how projects can allow "good" contributions without spending more time on weeding out bad ones, a blanket ban makes sense.