It's probably fair to say that portrait photography (as opposed to the more general class of "people pictures") presents a set of challenges not found in most genres.

While it is not possible to characterise the whole genre, portraitists are generally tasked with telling the truth, but not the whole objective truth. There are, of course, photographers who've made it their style to create photographs in a hyperrealistic "warts and all" fashion, where every pore and blemish on the subject's skin is paraded for all to see. At the other end of the scale, there is the romantic, soft-focus, painterly rendition that leaves everything to the imagination. Both approaches are legitimate, but very much a matter of taste and vogue.

Most of us, though, aim somewhere in the middle -- call it selective sharpness. We want the eyes, the hair, and (sometimes) the clothing to have a lot of detail, immediacy and presence. We also want the skin to look like skin -- we rarely want to make manneqins or wax figures of our subjects -- and want the shape and contours to remain identifiably and unquestionably those of the subject. At the same time, we want to avoid calling undue attention to flaws -- the zit that was there on the day you took the picture, but wasn't there the day before or the week after, a roughness of skin texture that is very much at odds with the character of the sitter (subject), lines that show clearly in the photograph but are much less noticeable when you see the sitter in person (particularly when emphasizing great age is not the aim of the picture), fine facial hair that you rarely notice except in detailed photographs, et cetera.

It is in removing or reducing those flaws that can't be addressed by lighting and posing that something like Photoshop and its like (and the plugins available for same) make their presence felt. Used properly, these tools will allow one to do away with the distractions without making the finished work look like anything other than a well-shot photograph.

Is it cheating? I don't know, but we used to do the same thing with pencils, dyes and bleach on the negative and the print back in the film days. My feeling has always been that a portrait is meant to portray the sitter (thus the name), and that there is a much greater subjective truth to be told in the portrayal than the mere objective truth gained by the process of fixing a pattern of light and shadow on paper. It is only very rarely that I find a "straight" photograph to be an adequate portrayal of the subject. I never actually lie; I just withold or gloss over those aspects of the whole truth that do no good for anyone. My opinion, then (and it is only an opinion) is that some use of competent image editing software is practically indispensible for portraiture.