You think that forming huge cities is the key to technology? "If we all band together, it'll be like magic *poof* technology"
You can have comfortable lifestyles in small communities. The one hurdle is taking our advances in manufacturing, and small scaling them down to fit community needs.
What stops communities from making laws? Nothing. If that's what they want, then it would be oppressive to not allow it. So long as they don't try to impose those laws by force on others. The essence of anarchy is lack of oppression, thats why it's technically about freedom, but you aren't "free" to horde things, attack others without reason etc. Thats the difference between mad max lord of the flies bullshit propaganda and real anarchy. As its not a national model, but a nation sized grouping of communities, you can't tell another commune what they can and can't do, and likewise, they can't tell you. Of course thats all theory, and no practice. Of course, this assumes everyone participating is volunteering to do so, at least for the first generation or two, otherwise they wouldn't have started a commune/joined a commune, but eventually, people may feel they'd rather have a hierarchy, for whatever reason, and as it's not national, they'd be able to do that, given the community doing so agrees. The alliance for defence and trade would be in place to stop them from trying to force others.
If suddenly 80% of the communes decide to pull a 180 and want to be a dictatorship, and force the other 20%, yeah, they are fucked, but that would happen in any system where 80% of the people want one thing, and 20% want the other.