On one hand, unpopular ideas are disproportionately likely to be advocated by disagreeable people. On the other hand, those who hold unpopular positions often have to defend their views and be familiar with the opinions of their opponents, while the proponents of popular views may not be familiar with the arguments for unpopular views. For example, outspoken atheists are likely to be more disagreeable, but they're also more likely to be familiar with religious people's arguments than the typical religious person is familiar with arguments for atheism.