Police, Protesters Clash Over Lekki Toll Gate

There was peaceful protests in Lekki today concerning the toll gate fees, until police stepped in and it became bloody. Some of the protesters were beaten while some have been arrested. 
Why should a peaceful protest become violent, can't the people speak their mind anymore?
You have read this article with the title Police, Protesters Clash Over Lekki Toll Gate. You can bookmark this page URL http://meditacaoplanetaria.blogspot.com/2011/12/police-protesters-clash-over-lekki-toll.html. Thanks!