Does Syria have a right to support Hezbollah?

In the first place,Israel continues to occupy the Golan Heights and refuses to negotiate it's return. In the second place,it is generally accepted that sovereign states have the right to support guerilla organizations. The US was not happy with Soviet support for the Viet Cong but we did not question their right to do so; similarly they did not question our right to support the Mujahedeen in Afghanistan in the 1980's although they could hardly have been pleased. Where does this notion proceed from that sovereign states such as Iran and Syria do not have a right to support extranational militias whose cause they endorse? The US does it all the time.