This is a good question to ask. Prospective and current PhD students need to understand the pros and cons, and the incentives driving their recruitment. But in

This is a good question to ask. Prospective and current PhD students need to understand the pros and cons, and the incentives driving their recruitment. But in terms of defining the problem, it all depends on your perspective... As a society, we are severely lacking in people doing deep dedicated study in important areas. Understanding biology at a level that allows us to alleviate much of human suffering is still a long way away, for example. So perhaps the question is 'Why do we pauperize people interested in doing serious science and then make them feel bad about it?'