So they're on the OWS path.
Their cause was just, their means was just not appropriate for the cause.
Taking over a Federal cabin even if it is in the middle of no where and uninhabited is no way to effect federal policy. Washington cares no more about the cabin than they do about any of the other western lands and people.
Taking over a small bit of it is nothing more than an afrount to their power, as unjust as it may be. The only thing you can do is force them to overplay their hand. Unfortunately this is not the right settling to do it in.
You have to be defending your own home in peace, to iliscit the sympathy of the people. Taking over federal property even that which is unoccupied, unjustly owned, and insignificant gives them the moral high ground by making you the aggressor.
Its best to make nice here, Explain that this was a protest and that your efforts to bring attention to your cause got out of hand. Then ask to leave in peace with a small fine.