So what you propose is that YOUR freedom of speech entitles you to call for a government to block facebook(if this is the case then of course you have that right)

But....

If however, that government acts on YOUR request then it denies EVERYONE ELSES freedom of speech. And your freedom of speech CAN NOT override anyone else's, and vica versa.

What you can do to exercise your freedom of speech, in a mature and civilised way, is to counter the event by engaging in spreading the word of your faith in a celebratory way on facebook on May 20th. There is already various Muslim campaigns set up to do this - just check out Youtube to find a myriad such posts; here is one such post:
http://www.youtube.com/watch?v=EkD9VRLl02E&feature=related