Thus far, there is no outrage in the Arab world, Europe, or American college campuses over this violation of Lebanon's sovereignty:
Rebels fighting the Syrian government are shelling villages on the Lebanese side of the border in order to curb a Lebanese group's efforts to help the Syrian regime. ...
The rebel Free Syrian Army accuses the Lebanese Shiite militant group Hezbollah of fighting alongside Syrian Army troops and has vowed to escalate its attacks against Hezbollah in Lebanon's northern Bekaa Valley. The Voice of Lebanon Radio reported Sunday that Jabhat al-Nusra, the Al-Qaeda-affiliated rebel faction, has warned that it will attack Hezbollah throughout Lebanon, including the party's stronghold in the southern suburbs of Beirut.
I'm going to guess that there won't even be any complaints about the "proportionality" of the Sunni firing into Lebanon.