Apart from the other suggestions offered here, I think that a large portion of the loathing comes from exposure solely to snapshots like these, whereas mundane conversations and actual research go ignored. When I was little I was clueless about communism. I remember repeatedly seeing German Fascism paired with communism, so I expected the CPUSA to be a hate group, but when I went to its Wikipedia page I was surprised at how progressive it looked (although I later learned that the CPUSA is a joke, albeit for unrelated reasons). Eventually I found the RevLeft forum and I was impressed with how chill the regulars were there, too.
Compulsory education failed to quench my natural sense of curiosity, so I spent a while lurking RevLeft and eventually Feddit’s socialist subcommunities. I checked out books like Is the Red Flag Flying?, Human Rights in the Soviet Union, and Inventing Reality. My politics shifted from a vulgar state-socialist, to anarchist against state socialism, and finally to anarchist who respects state socialism; I stopped condescendingly assuming that state-socialists were just confused and approved of the people’s republics out of sheer principle. It took a good deal of studying and some maturity on my part to reach the point where I am at now.
So I think that a large portion of the loathing comes not only from limited exposure but also from a reluctance to do more research, either because they lack the time, lack the curiosity, or both, which ultimately originate in how capitalism diminishes nearly everybody’s free time and damages our sense of curiosity.