I think socialism must fail because humans once freed from material want will compete for status. Status inequality will activate much the same sentiments as material inequality did. To level status one needs to embark on a massive value engineering campaign. These have so far always created alternative status inequalities, thus creating internal contradictions which combined with increasing material costs eventually bring the dissolution of the system and a partial undoing of the engineering efforts.

If technology advances to the point where such massive social engineering becomes practical and is indeed used for such a purpose on the whim of experts in academia/a democratic consensus/revolutionary vanguard... the implications are simply horrifying.