Collectivism vs individualism

Collectivism had become less popular when it failed so horribly during the 20th century. Fascism, nationalism and communism all contain collectivism, but here I'll focus on the logical reasons why collectivism is terrible, rather than giving examples.

The idea is that people can get better results by working as a group, even if it requires giving up some personal interests. https://en.wikipedia.org/wiki/Collectivism.

But what are the interests of the group?

It seems like an obvious answer, especially since everyone will have a number of idea's of what should be done. But in practice we find some serious problems:
- Everyone disagree's about almost everything, so when only 1 decision can be made a lot of people won't get what they want.
- Bribing/influencing can have enormous consequences because leaders are making decisions to spend other people's money and for a lot of people.
- When contributing to a democratic decision people are often making decisions for other people, not themselves. This allows for unfair decision making.
- "The greater good" allows sacrificing individuals for anything because leaders can claim anything to be in service of the greater good. The importance of such a good can never be measured, so any sacrifice can be justified if the leader feels it is.

Lets discuss the situation of the individual. People can determine their own interests very well. Exceptions like children and mentally handicapped are not relevant for this discussion, they can be helped by the other people. And if we respect each individual we've automatically respected the group. If we serve the interests of each individual, we've automatically served the interests of the group as a whole. People can, and often do, work together to achieve greater goals than just their personal interest. They don't need to give an authority power to achieve this.