The central tenet of our faith is that there is that of god in every person, so it follows directly that violence against any person is violence against god, and therefore unacceptable. Quakers have put their money and actions where their mouth is - they have always rejected capital punishment, and have been very active in prison reform since the 1800s. They set up the Friend's Ambulance Unit so they could serve during the Second World War. Quakers also recognise that there are many forms of violence, and sponsor the Alternatives to Violence Program (AVP) training for schoolkids.
To get back to the original question about dealing with violent people, of course you need to use force against them, to prevent them doing more violence. But that force should be as non-violent as possible, to make it clear that society's norms are intact. Norway's treatment of Anders Breivik is inspirational - it is clear that his incarceration is in no way violent - there is no element of revenge, much to many people's fury. But imagine a Breivik sympathiser - seeing a civilised society treating him in a civilised way leaves very little to spur them on to similar acts.
And what about Daesh? They have successfully used resentment against the violence done to muslims to build a society where violence is the norm. This is not sustainable - it won't be long before the flood of recruits reverses, as they discover what arbitrary violence means to them and their loved ones.