I would imagine that the primary reason anyone thinks communism will fail is that greed is too rampant amongst many people these days. I happen to agree, communism is nice to think about but I have worked for the state of California. I've seen what having a job that you do next to nothing at, get paid a liveable wage on, and basically can't be fired from has done to state govt. It's a fucking mess. These are people who, right now, are complaining about homeless people despite the only thing separating them is the fact that they were lucky enough to know someone who worked for the state. I mean it when I say they quite literally do nothing and get paid for it.
Cali state govt is socialist as fuck, and the outcome is things like millions of peoples information being leaked. We're talking social security numbers, drivers license, where you live, etc. If you can't tell me how you avoid the equivalent of things like this happening in a communist govt (because the outcome with communist govt corruption is worse by a large margin) then I just turn my brain off and stop reading.