Marx and Engels where both reviled by the mainstream liberals during their own time. Only in the late 20th century was Marx made like this kind demsoc grandpa that only stood for co-ops and liberal values who would have hated Lenin and Stalin "who obviously misunderstood him and Engels". It's also partly because of things like the new left and frankfurt school, Marx has his name slapped into everything from animal rights to art critique and other things that have nothing to do with class struggle and that has taken the edge off in the eyes of the liberals.
It's however absolutely right that all the bad communists, the vile dictators and authoritarians are those who stood up to the west and capitalism, fought the porkies, won, didn't get couped afterward and actually built something resembling real socialism. People like Lenin and Stalin are hated precisely because they succeeded and didn't get crushed by the forces of reaction.There is also the radlib phenomena where they are allergic to any contradiction in real living world. The further a revolution goes the more contradictions and problems there are to work through. So you can really be pure and represent "real socialism" if you never really tried or got a chance to put anything into practice or died a martyr at the early stages with untested ideas. If you succeed and have to test and develop stuff, fight and compromise you become a dirty creature of "not real socialism".