While it might be "romantic" to believe that the people can rise up and organize to fight these gangs, I think it is a little fantastical. Look at history, during the LA Riots, where there was a complete breakdown in social order. The people who suffered the most were Koreans who were left to fend for themselves. Even with their best efforts, damages were estimated to be $500 million.
It is exceedingly difficult to formulate a cohesive defense against the rioters for a variety of reasons.
1. The rioters travel. If you wanted to be patriotic, it is unlikely you will defend a district beyond your own immediate neighborhood.
2. The rioters are exceedingly well organized. This is likely due to foreign support. They are always able to get their hands on ample supplies such as gas masks, improvised weapons, and bring sufficient numbers to intimidate others. To make an effective defense, you need better planning, better organization, and it is just too difficult to coordinate this among regular people.
3. The rioters are younger on average. They have less to lose. Older people have business or family to worry about. The man who was burned has 2 daughters. Plus, look what happens when people organize to defend themselves in Yuen Long and North Point, smeared in the media as Triads. Then it opens up to more revenge tactics by the "Black Guard".
The "good people" are relying on the law to protect them. They are the people generally less fearful of government ("If I don't do anything wrong, I don't have to worry about them"). Even in the "Cradle of Freedom" USA, when LA happened, when Katrina happened, they had no problems with bringing in the armed forces to bear. What is the HK government's plan? This much you can't blame on the rioters.