Political Nihilism has never achieved anything and offers nothing to anyone. Likewise a "ruthless critique of everything existing" only achieves political inertia and smug satisfaction in armchair theorists as the world around them falls apart. How comfortable it is to criticise everyone else for trying to make the world a better place in which we find it, and how paralysing it must be to be afraid of having the same done to you. If you're not making mistakes you're not making anything.