This would certainly be a double-edged sword. You would presumably end up with a society that was more contented and less violent. At the same time, you may have a society that did not achieve much in the way of progress.
Happy people are much less likely to cause problems for society. They are less likely to commit crimes. They are also less likely to become ill because of issues like stress. They would be less likely to get divorced and leave children in broken homes. All of these things would tend to make society better.
However, there would be a tradeoff involved. Much of the progress we want in society can come from people who are full of ambition. Such people are generally not happy and satisfied. They have driving desires to get ahead and are not happy with where they are at this point in their lives. If all people were happy and satisfied, society would lack this drive and we might not have the same sort of progress in science and technology and the economy that we would like to have.
Overall, then, we would be likely to have a less violent society with fewer problems, but also without so much progress.