http://ratchasima.net/2007/09/21/the-anatomy-of-thuggery/

It explains some of the background to the actions taken by protesters. 
Throughout the country, there are well-known leaders of government-organized gangs which the government has been using to do its dirty work.  In Pakkoku, both the monks and the villagers knew exactly who these people were.  When the thugs attacked several protesters, including monks (possibly killing one), they incurred the wrath of the villagers.

And several monks, understandably angered by the thugs' brutality, also took part. This wasn't the wanton destruction some writers seem to be making it out to be; and the Burmese protesters are right to be wary of these hired thugs.

Furthermore, the events in Pakkoku must be separated from the events in Rangoon and other cities.  The protests in Rangoon have been non-violent; I see no reason to denounce these demonstrations because of the events in Pakkoku.

I am reminded of the peace marches of Preah Maha Ghosananda into Pailin, a Khmer Rouge stronghold, in the early 1990's.  These marches did their part to bring about reconciliation between former Khmer Rouge cadre and the rest of Cambodia.  Considerations of whether monks should be involved in politics aside, I for one would not have stood in his way.

Monks' involvement in politics can lead to harm (viz. Sri Lanka) and it can lead to benefit (as in the example given above of Maha Ghosananda).  I suppose it all depends on the monk(s) in question.