If we follow this line of thinking, we don't have to go far before we decide to force everyone to do exactly what we _think_ is right, justified by some hand wavy science or moral belief.

There is disagreement in society; we aren't all drones with a hive mind. One person's justification for what he thinks is best is just that, one person's justification. Someone else might think they can poke holes in his arguments, and who is to say which is right? No one. They can go about doing according to their personal beliefs.

There are some conventions in society, but once we start encroaching on the gray area, then society becomes oppressive to the minorities who dissent. Our society can clearly see older societies that did it, but fail to see when they are doing it. Just because you think you are absolutely right doesn't mean you have the right to compel others to do it. And, just consider, you might just be wrong... but of course not, our society is so enlightened, it couldn't be wrong...