Is Idealism Really a Bad Thing?

Lately I've been in several conversations where idealism is put down. Come to think of it, most of those conversations have involved the same person.

And, as someone who is greatly attracted to idealism - to characters in books, television and movies that display it, to people who demonstrate it - and who has a great deal of idealism in my own thoughts and dreams, I have to ask:

Is idealism really such a bad thing? I mean, wouldn't the world be lacking a lot of really beautiful things if various people hadn't been idealistic enough to believe that they could make a difference, that they could add beauty, in spite of opposition and naysayers?