my own position is that i don't think it's productive, and in most cases it's ideologically inconsistent with a rejection of property rights. i've never been in the situation where i'm standing beside somebody that smashed in a window. but, i think i'd be likely to yell at the person until they agree to reverse the damage. if i knew the person, i'd bug them for years until it got done. i'd argue that tort law is the ideal way to deal with issues of damage to personal property, or attacks on collectively owned property.
that said, i'd support the tactic if i thought it had some positive end point. consider smashing through a holding cell, for example. or destroying some carefully calculated political photo op.
as many others have pointed out, this is counter-productive and very difficult to spin in a positive manner.
but, i want you to take a close look at the participants. they're children. and, i'd suspect few really understand the issue. perhaps children looting a 7/11 is just that. nor should you be surprised when they steal slurpees and chocolate bars. they're kids.
this is a big deal, certainly. but i don't see a political protest. i see kids out of control.