Unless the 'thoughtful protesters' outnumbered those who advocate violence (or stand by and allow it to happen), then a few consciensious individuals will have no impact on what the rest of the mob does.

If you're a Seattle cyclist and you want to participate in something useful, Cascade Bicycle Club is working to bring together cyclists, city council and police to work toward an amenable solution. The following is quoted from their newsletter, "Braking News"

Some of you may have been present at Friday's Critical Mass ride in Seattle, and many of you have read media accounts of the incidents that occurred at the ride. Cascade Bicycle Club is not involved in nor are we affiliated with the Seattle Critical Mass rides. Our organization has always taken the position that cyclists must obey all the rules of the road. We also support law enforcement of bicyclists who violate traffic laws and regulations. We do not condone or support the unlawful behaviors that some riders choose to follow on Seattle Critical Mass.

It is our hope, and that of others, to see a de-escalation from this point forward. To this end, we are calling for a meeting of bicycle community members, law enforcement and city officials. Seattle is on the brink of great work in terms of bicycling, and we would like to see positive focus on these issues.
Read Cascade's full statement (PDF)