From an evolutionary POV, the number of past sexual partners is the number of women who 'voted' you to have mating potential. Women grant more weight to other women's evaluation of you than they do to what you think about yourself.
1. More women should be thinking for themselves and making their own decisions. Are they that unsure of their own judgment that they need to evaluate a man based on the imputed opinions of people they've never met, many of whom are in his distant past? I, for one, like finding a great girl who men have underrated in the past.
2. A low or high number of sexual partners has, in general, a lot more to do with lifestyle and values than ability.
And what we learn from evolution is we should laugh at should too. My theory: should is a gambit to control you on the part of other people trying to win in the game of evolution.
Thus, a woman benefits by selecting a loyal man rather than a promiscuous one. For her to marry a loyal man with strong genetics (e.g. an attractive man with a limited sexual history, indicating a low disposition toward promiscuity) is optimal. A woman who disqualifies men because they've had a low number of sexual partners is never going to accomplish this.
Anyway, the obsession over the number of past sexual partners means nothing in an evolutionary context, since the whole concept is a social construct. Pre-numerate cave dwellers would have lost count pretty quickly.
Anything's reproductive "goal", in any times, is to show up a lot in later generations. Promiscuity and particularity both show up as strategies in humans and broadly beyond. Anybody studying reporductive strategies many generations later will have a strong survivorship bias in their results.
A woman who selects a man who isn't very promiscuous is unlikely to get her genes spread very far by her son(s). This trades off against the part of the story you tell.
Primitive strategies are none the worse for being primitive: though no guarantor of success, they're often adequate. thus the number of citations of a science paper is not a direct reflection of its quality, but not irrelevant either. I was surprised to discover that market traders, far from being tight-lipped about their strategic overview, spend a lot of time calling each other up when things were slow to ask what their competitors thought of the day's financial 'weather'. Google's Pageranks are similar. And so on.
It is true that a fairly non-promiscuous person will likely be a better parent and thus a desirable match. Nevertheless, some competitive genes don't hurt. Also commitment after experience is more interesting than commitment by default (see daily YC thread on how 'Windows users only like it because it came with the computer they bought').