The last line of Marx's Communist Manifesto is "Workers of the world unite."
Since the manifesto calls for people to unify in a struggle, I suspect that many falsely concluded that Communism is an ideology of unity.
The truth, of course, is that Marx was seeking to raise a group of people in rebellion against a defined enemy: the bourgeoisie. The term "bourgeoisie" refers to the middle class. The goal of Marx was to unite the ends against the middle.
I suspect that there is a large number of people who sincerely want to be part of a unified force. The problem, of course, is that all of these unified forces have something that they are against. Political efforts to unify people on an issue almost always creates a reactionary force.
In the rare instances that we do achieve unity on an issue. There is almost always someone wanting to push the unified collective onto a different more divisive issue. For example, we may be unified in thinking that dog fights are barbaric. There will be voices that want to use the unifying issue against hunting, or eating meat.
I find the free market and democracy more compelling than Communism. These systems create a structured mechanism for division.
When coming across calls for unity. One should recognize that almost all calls for unity are seeking to unite people against something. Although such calls use "unity" as part of the rhetoric. It is difficult to say that such efforts really are leading to unity. In most cases they lead to a division at a deeper level.