One thing that definitely plays a role in this discussion is that in big street protests, a lot of people have to come out of their house and basically waste their day for this one cause. This in itself shows how strongly they feel about certain issues.
This is much more difficult in the case of internet protests: we all know how little facebook likes mean.
If you want to make web-based protests work, you will somehow have to incorporate an element of effort, which - since the only tissue we have online is that of information - is going to have to have some intellectual ingredient. Indeed, the many discussions we are having on this very website can be seen as minor protests.