Let's not forget these people had every intention to use those weapons against humans. This isn't some guns club hanging out.
That being said, they were looking to defend themselves while illegally occupying a federal facility... but the particulars of that situation don't really reflect on the choice of weapon.
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.
Then again they overtly sought to institute their own court system, and overtly sought to subject government officials to trial for various crimes by that court system, and issued threats for non-cooperation with that effort, so its not at all clear that the end game, were they not arrested before that escalated further, wasn't "hunting down people and assaulting them".
The only speculation is that they would, if not constrained by intervening events, carry out their overt threats in support of their overt goals. That's not a lot of speculation at all.
Not with the guns, and not physically, much. But they most certainly were threatening people, according to the FBI complaint against them:
"The person with Ritzheimer told the woman he knows what kind of car she drives and he was going to follow her home and burn her house down, according to the complaint."
No it is not a defense to say that they are defending themselves. These people illegally encroached property that was not theirs.