Armed clashes happened as some of the masked youth opened fire on the regime forces by injuring several of them before escaping from the area. It's started. If the regime thugs are now personally at risk, it will dampen their enthusiasm for going around trying to intimidate people
I'm surprised that we haven't seen more armed resistence by the demonstrators. Even if they haven't access to guns, the use of knives, spears (knife taped to stick), and Molotov cocktails would allow them to GET guns away from regime forces. If they force regime thugs to always have to move in armed groups of 50 or more, then there won't be enough thugs to stop demonstrations.
...I'm surprised that we haven't seen more armed resistance by the demonstrators. ...
Most of the leaders inside and outside of Iran are counseling the demonstrators to use non-violent forms of resistance. That does not mean the demonstrators should not protect themselves.
I believe the concern is that armed clashes concern the pro democracy movement because they can easily be out gunned and fear losing what little international support they have.