https://www.bbc.com/news/world-europe-53039864
(Duda was born 16 May 1972, so he ought to have some personal experience of their relative "wrongness")
At a micro level, communism saps the entrepreneurial energy from economies as it relies on the state to determine what goods and services should be produced. It also potentially acts like a disincentive to work as work is performed for the national well-being not the personal well-being. Not that all individuals reject the notion of patriotic work for the betterment of the nation but I feel that more are incentivized by personal rather than patriotic rewards.
Traditionally, communism leads to the restriction of movement and voice for the citizenry. Any system that needs to erect laws and walls to keep its own citizens from leaving or voicing their displeasure seems to be a system that is fundamentally flawed. I am not saying that any other "pure" ideology (particularly free market capitalism) is without faults, but you asked specifically about faults related to communism.
"The bourgeoisie cannot exist without constantly revolutionising the instruments of production, and thereby the relations of production, and with them the whole relations of society. Conservation of the old modes of production in unaltered form, was, on the contrary, the first condition of existence for all earlier industrial classes. Constant revolutionising of production, uninterrupted disturbance of all social conditions, everlasting uncertainty and agitation distinguish the bourgeois epoch from all earlier ones. All fixed, fast-frozen relations, with their train of ancient and venerable prejudices and opinions, are swept away, all new-formed ones become antiquated before they can ossify. All that is solid melts into air, all that is holy is profaned, and man is at last compelled to face with sober senses his real conditions of life, and his relations with his kind.
The need of a constantly expanding market for its products chases the bourgeoisie over the entire surface of the globe. It must nestle everywhere, settle everywhere, establish connexions everywhere."
— Marx 'Communist Manifesto'
From a formal point of view, Communism can be considered one of the purest forms of democracy, which makes it susceptible to the largest problem every democracy has - the people. Any democratic society relies extremely on the people's good will, (social) responsibility, and education. That makes it also the most fragile state form possible - as soon as even one of the criteria fails, the society inevitably changes. It can be a more or less slow evolution into an aristocracy or a monarchy, or a rather revolutionary change into an ochlocracy, oligarchy or a tyranny.
Imagine being declared scum because you own a business, and having almost everything taken away from you.
there were exceptions, but even the better working conditions were so far below today's standards that calling e.g. the factory owner "scum" would actually be way too mild.
It is not a historically correct view that only those business people who matched evil stereotypes from Charles Dickens novels were targeted for dispossession, and everyone else could continue on as before.
It simply became a crime to own property pretty much beyond personal belongings.
Your own little farm, book store, whatever.
Talk to anyone of Chinese descent who got on a boat and the hell out of Vietnam when the communists won the war.
Speaking of descent, these communist takeovers have been tinged with racism/xenophobia. Whereas in Vietnam it was the Chinese elite with money and education, in the The Soviet revolution, the situation was heavily anti-semitic since a lot of the business owners were Jews.
Modern liberals in America, especially anyone too young to remember and relate to the cold war are, know basically fuck all about any of this. No first hand account of anything, just indoctrination from politically-correct sources.
I myself am a refugee from former Czechoslovakia. I actually lived in communism.
Ironically, now I once again may not criticize communism. Wait, that's not even what I'm doing. Rather, I may not make uncontroversial, true statements about communism that Stalin would likely agree with if he were here.
In truth there is nothing wrong, per se, with Socialism, Capitalism or Communism. Merely the way in which they are implemented.
There is no country in the world that does not have a mixed economy, with facets of all three Socialism, Communism and Capitalism interspersed. Sure, there will be weasel-words to prevent the truth coming through, like 'Common Good' instead of 'Socialism'. But one country's 'Common Good' is the next country's 'Socialism'.
(Roads and Highways, Single-Payer Health Care, Unemployment Assistance, Food Stamps, Business Bail-Outs, etc, etc.)