There will always be people who will steer away from bad behavior in the absence of rules. Some people's basic nature will always lean toward acts that are considered to be good or positive. Just as there are some people who's nature will force them to lean towards evil, even if they've been surrounded with nothing but positive thoughts and energy.
What rules are necessary for are to be temptation squelchers. We are more likely to slip up and do wrong when we believe no one is watching and that there will be no subsequent consequences. For instance, if a person is driving their parent's car, the level of driving will vary, depending on whether they are alone, or that parent is sitting beside them. Societal rules are like having your parents beside you when you're driving their car.
Subsequently, a world without rules is a world without order, and though most people are decent by nature, we need rules to help resist the urge to revert to our animalistic, primal selves. One need only see a room full of unsupervised children to be reminded of the true and overwhelming fact that the true order of the universe is chaos, and order exists only when forced.
Often enough, in the absence of societal rules, people will often apply their own "individual " policies. That is, policies that are designed to benefit the creator of the policy, yet be of great detriment to others. Case in point, the cult leader who declares himself God, then demand that his followers turn over all their worldly positions to him. He in turn goes out and buys a fleet of luxury cars for his personal use, while his followers have to walk everywhere they need to go. Cult leader gets to decide for everyone; cult leader decides everyone but he should make do with the less than finer things in life.
Another less insidious example would be the supermarket free sample table. If a table of free samples is set up, and there is a person standing there monitoring it, people will most likely take one sample and move on. Yet, if there is no monitor, just a sign that says "Help yourself", I assure you there will be few people whose pockets will be bursting at the seams with free samples. I reiterate, if no common rule is established, people will almost always set things up to their favor, yet to the detriment of others. Humans are tragically flawed that way.