As to only picking soft targets there was nothing soft on the CIty parade - right through the banking sector outnumbered by police - against the odds that day. This is ultimately a symbolic and demonstrative action though remember - banging on some windows isnt going to make the buildings and institutions disappear...
One thing thats a bit weak at these is little to no attempt to connect with people and bring them on board. Seems the philosophy behind this is simply to be a mob, and those naturally sympathetic are drawn to the mob and don't need anything explaining to them. It may not be the most effective model, but it is what it is - and as Martin Wright points out, theres an ancient tradition of it. It is what it is, and its pointless asking , why not do this and do that.