They are already there.
Since 1978, the UN has had UNIFIL (United Nations Interim Force in Lebanon) set up. And since 1978, they have not lifted a single finger to stop rocket attacks towards Israel.
Since then, they have not lifted a finger to stop Hizbollah from building a full army under their noses.
Since then, they have not lifted a finger when Hizbollah built military posts right next to UNIFIL posts.
Since then, they have been sipping tea with Hizbollah, they witnessed the fatal kidnapping of Israeli soldiers in 2000 and refused to even help in the investigation, and they have failed miserably to live up to their mandate:
* Confirm the withdrawal of Israeli forces from southern Lebanon;
* Restore international peace and security;
* Assist the Government of Lebanon in ensuring the return of its effective authority in the area.
In other words, they have been firm supporters of the terrorist Hizbollah organization and firm enemies of Israel (as well as Lebanon.) But Lebanon found them useful as well, because as long as they were in Southern Lebanon the Lebanese army could pretend that Hizbollah was not their problem.
Combine this with the fact that the UN refuses to declare Hizbollah a terrorist organization (perhaps they are a origami club?) and you have a completely immoral organization lecturing Israel about morality.
H/T Atlas Shrugs
As Jed Babbin writes:
The U.N.'s years-long record on the Israel-Lebanon border makes mockery of the term "peacekeeping." On page 155 of my book, "Inside the Asylum," is a picture of a U.N. outpost on that border. The U.N. flag and the Hezbollah flag fly side by side. Observers told me the U.N. and Hezbollah personnel share water and telephones, and that the U.N. presence serves as a shield against Israeli strikes against the terrorists.