What is unrealistic idealism?

I'm not sure if you are trying to define this for a class, so I may not have the definition you are looking for. However, just going by logic and the basic definitions of the Words, I can give you the following:

Something unrealistic is not real or practical. Idealism is the pursuit of noble principles. Therefore I would think that unrealistic idealism would be principles, ideas, goals, etc. too far-fetched and lofty to achieve in the real world.