When socialists call billionaires a parasite class, they're often describing the role they'd prefer for themselves: receiving the benefits of production without bearing the risks, costs, responsibilities, or sacrifices involved in creating it.
The entrepreneur risks failure, invests capital, delays gratification, organizes resources, and may lose everything. The socialist critique usually ignores that process and focuses only on the reward.
What many socialists object to is not consumption without production. Their politics often centers on expanding access to wealth created by others. What they object to is the producer retaining ownership of what he helped create.
They condemn profit while demanding the products, services, technology, medicine, and prosperity that profit helped make possible. They attack the incentives that generate wealth while treating the resulting wealth as something that should simply exist.
The irony is that those most hostile to "parasites" frequently direct their anger at producers while demanding greater political access to the producer's wallet. The dispute is rarely about parasitism itself. It's about who gets to control and consume the wealth once it's been created.