That Lebanon has the right to protect its territory, because it is supposedly a sovereign state. On the other hand Hizbollah is not a sovereign state, but rather a terrorist organisation usurping the rights of the Lebanese state and oppressing many Lebanese that don't share their malicious religious faith. In effect Hizbollah is a state in a state, and has nothing to do with Lebanese sovereignty. Israel has every right to halt the flow of arms to Hizbollah, and even the Lebanese government is obliged to disarm these shi'ite terrorists on their soil. The Lebanese government though is unwilling and incapable to implement this, so Israel has to do it in order to protect its citizens, whether this will amount to violations of Lebanon's sovereignty or not.
Iraqi police fire tear gas as thousands of protests burst into Green Zone, storm Parliament (AP)
from the article: Netanyahu hints Israel will prevent Syria transferring arms to Hezbollah