People seek expediency by default because our brains are wired to expend the least amount of energy possible as a route to efficiency.

So, people delegate governance and thus we have the rule by majority.

In my opinion It is immoral only to the extent that the minority individual cannot freely leave if he disagrees. In a free and open world , an individual could just leave if he disagrees with the majority. There are many barriers to doing this today, so leaving often isn't an option.