While we all want to do something for Leiby. The Yetzer Harah argument is a red Herring, you can use that for almost anything.
For example why not ban CARS because of the Yetzer Harah, People want a NICE car when the money could go to tzedakah. People look at cars totally UNTZNIUS. Sometimes a nice car will get more looks than an untiznut woman.
Lots of things go on in cars that are assur.
People sometimes even drive as leisure because they like to drive totally bittul torah.
The car has a radio with assur music and all sorts of forbidden stuff on it.
I am not trying to ban cars, but if you subsititute Facebook with cars you can pretty much get the same discussion.