They believe in an authoritarian government systems. Where the state has extra power that they can use to enforce their goals. That is in contrast to anarcho communists where the state is dissolved.
Logically most leftists fall somewhere in the middle as not wanting full on authoritarian government but also not wanting a complete lack of government
In theory if the state has the best interests of the people, then by giving the state extra power all you are doing is reducing bureaucracy and increasing efficiency. That however also makes it easier for the state to abuse that power so I am not saying one is better or worse than the other