Citation needed on the binding rules claims.

> What is illegal is for all the companies to get together and make a binding rule saying nobody can buy ads from someone. That is conspiracy.

IANAL, but that seems... incomplete. Conspiracy to what? A conspiracy-to-X involves an agreement between parties to commit an underlying act X that is itself already unlawful. The idea being that mutual agreements are enough to show you "started" to do X, instead of merely just thinking about it.

So the X here would have to be something else that's illegal on its own, or else the charge would be its own kind of thing like "anti-competitive practices."

Every source I've seen has explicitly stated that GARM was voluntary, not required of members.