Ok so first of all whatever landlords do isn't "work". But apart from that, the distribution of labour in a planned economy is still very much a concrete problem that has to be solved mathematically. In socialism, people will still need to work X hours a year, even if X is now determined by their mental or physical aptitude, the difficulty of the labour performed, the progress of technology, or external conditions; and this X has to be determined in the central planning agency in a calculation that cannot be circumvented by moral philosophy. I'm not saying we can do the same sort of computation for the minimum possible amount of "bad" in the world, morally speaking, but to quantify labour is possible and indeed necessary in order for scientific socialism to be realised.