Mormon understands the real threat Amalickiah posed, even though his followers did not. First and foremost, Amalickiah was a threat to the church. Even though his ambitions were for the throne, the ultimate problem was not political, but religious. As king, Amalickiah would follow the Lamanite model, not that of King Benjamin, thus destroying the undergirding egalitarianism of Nephite religion. Once that principle was gone, the rest of the belief system might easily follow as Nephite society adopted the religious philosophies that supported Mesoamerican kings and their hierarchical societies.
It is less clear how Mormon saw “the foundation of liberty” threatened. I interpret it as the liberty to believe in Yahweh. Certainly the new king as a political leader would not have less liberty that Benjamin and Mosiah did. Even in the Mesoamerican hierarchical society, the kings provided benefits that the people wanted or the people’s service stopped.