I’m really surprised this hasn’t happened yet.
You need to tie your Facepunch account to a Steam account.
You need a Facepunch account in order to play Garry’s Mod.
If you’re banned on Facepunch, you can’t use Garry’s Mod.
Seems the right way to go.
Really would help weed out some people that don’t belong. Could be used to tie things to a Facepunch account, ie uploads.