This is very similar to an argument that libertarians make about their opponents. As long as the government is made up of benevolent geniuses with perfect information about every individual citizen, then socialism is a great idea. In reality, individual preferences are unknowable, and government workers are fallible and have motivations of their own.

In reality, neither utopia is particularly achievable in the world as it currently is, but that doesn't mean that incremental steps in one direction or the other can't improve the situation.