If pessimism is despair, optimism is cowardice and stupidity. Is there any need to choose between them?

The important part of Marxism was its demand for active, constant, practical, class-war

Rationalism, which is the feeling that everything is subject to and completely explicable by Reason, consequently rejects everything not visible and calculable.

Liberalism is Rationalism in politics.

To the fantastic mental illness of Rationalism, hard facts are regrettable things, and to talk about them is to create them

If pessimism is despair, optimism is cowardice and stupidity. Is there any need to choose between them?

Pessimism only describes an attitude, and not facts, and hence is entirely subjective.