I read it as "the left should do what the right is very successfully doing." One can disagree about whether this is the right course of action, and I'm not really confident it is. Just to play devil's advocate: I would note that common "norms" of behavior often come into existence because a situation develops where both sides take arms against the other, and in these cases it becomes optimal for everyone to disarm -- hence the "norm" develops. If you view this kind of behavior as one version of "taking up arms" then maybe it's necessary for all sides to engage in the behavior before the norm reasserts itself.