You can destroy the barracks that are useless to you and earn some money from it. I think the barracks itself have mentioned it.

The 99% damage governments are intended to be destroyed so you cannot cheat but need to build your own government building. But because it is hardcoded I think, the engine doesn't allowed it to be totally destroyed, so you need to do it manually. The reason why there are 5 types of governments is because or may be the settlement had been conquered by several factions, so they build their own government, but ai cannot destroy it manually unlike us, the HUMAN.