And if you let them alone, they will cut each other's throat.

This is not just a way of speaking. Communists are exactly like that. Check the story of the 'communist paradise' of Bulkes, where they soon ended up in a brutal civil war killing each other with accusations of fascism and activities against the Party:

https://cosmosphilly.com/bulkes-greek-republic-never-existed/

(The article provides a pretty idyllic view of Bulkes, as some of the protagonists wrote about their first hand experiences like throwing their 'comrades' into wells.)