How can "a lot" of a group be "purely" both "self-interested" and "idiots"? I do not think this statement can be anything more than rhetoric and schoolyard name

How can "a lot" of a group be "purely" both "self-interested" and "idiots"? I do not think this statement can be anything more than rhetoric and schoolyard name calling. I would say people have a strong interest in themselves and their personal welfare. This should be expected or we would probably not exist as a species. However the interesting thing about humans and some other intelligent animals is that they are also interested in the welfare of others, including non-relations, and even other species (some argue that this is part of a broader form of self-interest like the golden rule). However none of this should deny that people are motivated by self-interest most of the time. While libertarians talk about self-interest more than most I don't think there is any good evidence that their actions are any more selfish than non-libertarians. I would suggest they are simply making an observation about human nature that explains a huge fraction of human behavior.