Raising a family ties people down. If it’s a contest between a set of people whose primary occupation is raising families and another set of people with killing and looting as their mode of existence with either group having access to the latest weapons (the latter, in fact, able to afford more for weapons because these are their primary tools) the latter will always win. There’s a limit to how much resources a person can dedicate, if he or she also has family to take care of. Increasing these resources requires large scale pooling, which inevitably leads to government. The farmer’s taxes go into funding the army that’ll protect his property from enemies afar.
While I agree with what you say, I am curious what the results would be if the original band of thugs, some were quickly killed with the remainder given quick vigilante trials and hung for all to see. I think that would temper the desire to become a roving thug for a good 20 years or so.