One argument that I tend not to hear very often but occasionally stumble onto, is the accusation that Communism or Marxism is akin to a religion, that is, something based on faith.
The reason this is used strikes me more like a way to hit a soft spot on an Atheist or skeptic, rather than an attempt at true argumentation. Indeed, such a claim does not tackle any of the core tenets of Communism such as the labour theory of value, the explanation of capitalist shortcomings etc, but rather takes a generic shallow look at the history of attempted Communism and draws conclusions from that.
So let’s see what the arguments might be.
It is not based on science
Communism as any other socioeconomic system is not based on the scientific method. The scientific method requires an observation to happen before it can create a theory but you cannot observe a system that does not exist yet.
Capitalism is not based on the scientific method either. It did not come about because some scientists sat down and observed the current feudal system and found out that capitalism is a more optimal choice. No. It first came about and then the pseudo-science of economics set out to find out the rules that control it.
If anything else, Marxism is a absolutely materialistic philosophy and considers that only science can discover the truth about the world. In this regard, it is diametrically opposed to any other religion.
It is based on faith
As a completely faithless person, such an accusation seems absurd to me. For something to be based on faith, it needs to be believed regardless of conflicting evidence. But no such evidence exist against Communism.
This is doubtly untrue since things based on faith tend to be hammered onto the minds of children in order to stick. The enemy of faith is reason. Certainly it is possible that someone is brainwashed as a child to be a Communist, but such a person would be a very poor example of one as for Communism to work, it requires conscious, skeptical, critical and active people who can take action into their own hands and be willing to cooperate with others democratically. A passive, brainwashed follower might be fitting for a Stalinist regime but can never be considered a Communist unless he starts accepting the theory based on reason instead of faith.
Personally, I was always very critical of Communism for the same reason everyone else in the world is. Misunderstanding of what it really is. I only started accepting it once I dug a bit deeper and started criticizing my own preconceptions.
It is evangelising
This is the accusation that, like any religion, Communism requires people to spread the knowledge of it to others before they can accept it.
Like any idea before it, there is no way to spread it except through discussion with people who know about it. The idea of Capitalism, markets and merchants did not spread itself. Humanity did not begin with a part of it being merchants or capitalists. These classes of people were created when someone thought of the concept and then started spreading it to others, thought words and actions.
If this is a definition of a religion, then any idea is a religion.
It has a holy book, prophets and apostles.
This is absolutely untrue by the common definition of those terms. The Communist Manifesto is simply the expression of the part of an idea and as such it is subject to improvement as any other idea. It is not a dogma. The people who accepted Communism and spreaded the word can no more be called Prophets than Adam Smith who spread the idea of Capitalism. Nor can leaders who accept one idea over another make that idea a religion.
It is very easy to stretch the meaning of words in order to make a term less positive to the people who might embrace it. But this is a dishonest tactic. If one wishes to tackle Communism, the best way to do so is through rational dialogue on the actual points it proposes. Like any philosophy and idea, there will certainly be people who are dogmatic about it, but that does not describe the philosophy as a whole.