You're saying you want Antifa to be legally able to own/carry weapons?  POTUS could designate them a terrorist organization tomorrow.  Is a law currently on the books that prohibits members of terrorist organizations from legally owning/carrying a firearm?  Then that's all it takes.  Otherwise we might have another civil war on our hands...the shooting kind.  Not good.  I know what you're saying about speech but the exception there is not being able to scream fire in a crowed theatre.  Warranted and necessary.  I'm making a similar point with firearms.