Actions can be punished.
That’s not free speech. If you’re recruiting to kill innocent people, yes should be held criminally responsible.
We’re not talking about people joining a legal political party or NGO here.
That’s what I think but our lawyers, judges, and politicians have wussified our legal system over generations. Remember that communist parties worldwide were/are devoted to the violent overthrow of govts, yet I don’t think we have been able to outlaw communist parties or criminalize recruitment to them. They are essentially terror groups too, the worst of the 20th century, yet we allowed them to operate with impunity.
I’ll be glad if we criminalize recruitment to jihad groups but I’m not sure it has happened very consistently, at least.