Here's a simple explanation:
Capitalism is anti-social; a predatory economic system based on benefiting the one and or the elite. Socialism and Communism are social economic systems based on benefiting society or the many.
Now if you're setting up a society, do you want to promote an economic system that pits everyone against each other, or an economic system that promotes everyone in that society, generally, for the best outcome for everyone?
Anyway, people can probably guess your answer.