I think all of Subaru's deaths seemed to have warped your idea of what violence is. Knocking him out IS violence. Imprisoning him all tied up like a pig and blindfolded IS violence. He broke out because he was imprisoned unjustly (and meaninglessly in his POV), not knowing what they will do to him.
How the heck did you come up with "the non-violent solution has failed" from all that, I have no idea.
Ram took a fighting stance because Garfiel clearly gave an ultimatum (using that idiom) of surrender or get attacked (and clearly as we've seen, getting attacked means death).
Also, asking someone to surrender (and get imprisoned again) under the threat of violence is NOT a discussion. It's coercion. And that is not okay.
As for Subaru being suspicious, I absolutely agree. But suspicion doesn't warrant what Garfiel did. Remember, Subaru hasn't done anything harmful to them or anyone at all. They should've just questioned him more to know more, not lock him up and leave him alone without trying to learn anything.