Right.
Carrying a firearm = self defense. Fine. Someone might attack you, you can defend yourself.
Occupying land that is not yours = protest action. Fine. You'll probably get arrested or at least sent on your way, but fine.
Occupying the land AND carrying a weapon to defend yourself isn't just like "oh man, if someone tries to rob me during my protest operation, I'll be able to defend myself!" No, it's tacitly admitting that people are going to come and arrest you, and you expect to put up a violent fight.
Nobody's under any illusion that the police are going to march in there, put handcuffs on everyone, and walk out.