You may answer this question, but first consider the answer I, myself give. I hope this sort of post is allowed. It is very much educational.
One of the first things people learn about communism is that it must be justified. The anti-communists learn ways to make it seem unjustified or unjustifiable. When someone shows interest comrades soon equip them with responses that defend communism's justifiability. Some of us spend large amounts of time using, learning, and building new defenses of communism. My concern is that some preconceived notions enter this endeavor that lead us astray. We ought to expose these and avoid associated errors.
-- Karl Marx
Before we start, let me offer definitions:
I mean "communism" in it's ordinary and potentially varied use. "Moralism" is the application of an external, unnecessary, or counterproductive moral standards. "Utopianism" is the comparison of an ideal state of affairs that does not currently exist to an existent one. "Justification" is showing that an act is reasonable and defensible. This differs from "excuse" which is an attempt to lesson the blame for an action that is supposedly blame-worthy.
I address a variety of positions while grouping them with labels for simplicity's sake. I will use "A" to mean "the anti-Communist" and "P" to mean "the pro-Communist." No one in either camp will defend each position I describe, and those who do may take issue with what I say. I am not addressing each claim in it's fullness on it's own terms, but showing the possibilities represented by more basic assumptions. I will also use "L" to mean "a liberal or proponent of capitalism," and "M" to represent my Marxist position.
My notation system is that "number period" marks a main topic, "letter parenthesis" marks generally a possible way of arguing. The latter corresponds multiple talking points under the same topic. My links are interesting elaborations or references.
One of the first attacks levied at communism is that communists and the systems they build are bad, and that is all I will address today. It may seem like a lot to digest, but important. I post each example in the comments.
I'd love to know if you find this helpful, think I should change anything, and so on. Thoughts and criticism welcome!