A good question, Xandi. And I think for every two people you will get three different answers. People object to postwork for different reasons, if only merely for the reason that there are different kinds of postwork. Postwork might be necessary to correct deficiencies which might be avoided by better preparation, better lighting, better shaders, etc. These faults are far better corrected in prework (I think Paolo would agree with this). The reason for that is that correcting, for example, render noise in postwork almost always results in deterioration of the image—loss of definition, smearing, etc. On the other hand, if your postwork is to deliberately create unnatural effects that cannot be created in a pure render then that's an artistic decision, and I would not fault it. A number of artists consider the basic render as a starting point upon which they can apply their own paintwork. Nothing wrong with that in my opinion either, and well known photographer artists take this approach as well as 3D artists.

I don't have any particular skill as a painter so I try and complete my image in the rendering, but I do take a pragmatic approach. If I can improve my render overall, even though my postwork may create some deterioration, I will do so. I'd rather have a satisfying final result with postwork, for all the faults that may cause, than an unsatisfacory looking but "pure" render. There is a similar diversity in approach with photography. There are photographers that insist that the the whole frame should be printed and that no cropping is done, that all the composition is done through the viewfinder, and that no dust specks or such are spotted out, no exposure corrections, dodging or burning, etc. However, these are in the minority, and although it goes without saying that good photographers do their very best to create a great photograph from the outset, most professional work will have entailed some post production at least.