So what if he was selling kits?

It's legal to sell kits along with instructions for modifying a firearm from semi-automatic to automatic fire, and the results of that have been several mass shootings.

So modding your console or selling tools to do it ought to be legal as well. The damage from that is far, FAR smaller than even a single mass shooting.

A YouTube got 5 years in federal prison in 2023 for selling kits to convert a semi automatic rifle into a full automatic. In some cases you can be prosecuted just for possessing all the component parts to covert your rifle, much less selling them with instructions.

A tiny plastic 3d printed “glock switch” is itself actually classified as a machine gun under the law.

I don’t think that’s the case actually - there was a case recently where someone got sentenced to jail time just for selling a template that could be used to do so: https://www.justice.gov/usao-mdfl/pr/youtuber-and-auto-key-c...

A modded fully auto is likely less dangerous in practice, because you will burn through all your ammo without being able to aim properly.

This isn't to handwave away the horror of mass shootings, but most mass shootings are gang related, and largely by those already breaking a number of laws including owning a firearm illegally for those with felony history.