I just can't understand how idealism can be a bad thing. How it's somehow horrible for a person to be an idealist.

Being an idealist means that you think the world can be a better place, and that you're not going to just accept it how it is. That things can be nicer, safer, cleaner, or friendlier than they are now.

To me, being DMan's anti-idealism makes it sound like he wants things to stay how they are now! That believing that world peace is possible is not just unrealistic, but harmful, and that we should want war. Or that we shouldn't try and eliminate disease, poverty, homelessness, or hate, but should enjoy them being here.

If it's what the idealists are wanting that is in contention, then that's fine, I can accept that, because everyone wants something different. But if it's just the plain idea that someone believes things can be better for everyone (not just better for yourself) that you have a problem with, then I feel that person is nothing but a negative force in the world and will never do any good for anyone or anything. Just make it clear whether it's idealism, or the ideals being focused upon.