They don't care if it works. They only care if you give them power on the promise that it will. When it doesn't, blame 'the other side.' rinse, and repeat. Socialists know they can't make it in the real world without it; for them, power is survival, their struggle is for life itself.
This is why they struggle; it's not "social justice" or equality; it's THEM being richly compensated for dispensing their ideas of social justice and equality, only so long as it leads to more power, whether anybody likes it or not doesn't matter. To a Democrat, first, last and always, power is a matter of life and death. If that means yours in the process, so be it.
Why not - it worked for the Stalinists.