>>174324
is a very complicated subject, and it will require an entire essay. So basically, idealism goes against reason, (here you can read Critique of pure reason from Kant if you want to understand the idealist viewpoint, if you can read it because Kant don't know how to write). And idealists hate reality, that's why they are called idealists, because they believe in a ideal, an ideal who needs to be pursued. (the Übermensch on Nietzsche for example). Think of all ideas that comes with idealism: democracy, communism, liberty, human rights, perpetual peace, nationalism, feminism, hope, pacifism, justice, morality etc...
Idealism is a fantasy world, and a fantasy world should stay in the books. Idealism is incompatible with reality, and will only end up in failure.