The major argument for the idea that we should not rock the boat is that we should not be too arrogant about our own powers of judgment. If we rock the boat, we are essentially claiming that we are superior to other people.
When we rock the boat, we are going against the judgment of the majority of the people in our society or at least in whatever social milieu we find ourselves in. Our society or our smaller social setting is based on a set of rules and ideas that have been negotiated between people over a long period of time. These are rules and ideas that have been proven to work.
When we rock the boat, we are essentially saying that our judgment is superior to that of all the other people who have come before us. We are saying that our judgment is superior to that of our peers. We are saying that we do not care about the rules that they have set up because we know best. This is, arguably, a fundamentally arrogant thing to do. We should not rock the boat because we should be humble about our powers of judgment and we should be aware that we are capable of making mistakes.