Attending Protests

Just wanted to know, is attending protests permissible?

for example this one today?

http://www.cageprisoners.com/campaigns.php?id=791

As far as I know, the scholars differ on the issue, so do approach with an open mind.

Sorry, but that's all I know, really.

Why would protesting something be haram?
Of course I'm talking about something that islam approves of, not like protesting to make drugs legal or anything like that, but for something like this, one would think it would be all right?

Those are just my thoughts/opinions though, they don't matter, better ask a scholar.