Sex seems to have two main purposes. The first is immediate, and that is pleasure. The second is procreation, which seems to be the overarching goal of sex, at least from an evolutionary perspective. The argument could be made that sex is pleasurable because that acts as an incentive for us to have it, which then results in a propagation of the species. In other words, we are driven to procreate (on account of sex feeling good) whether we are concerned about propagating the species or not. In a sense, we have been duped by evolution - except that, generally speaking, propagation of the species is also within our interest (although in most cases it's not as pressing a concern as wanting to feel good).
However, as an intelligent species, I believe it is within our natural rights to exercise some control over when and whether we procreate. Evolution may want us to procreate as often as possible, in the hope that an abundance of offspring will guarantee that some of it survives, and that the resulting diversity will improve the species' adaptability to changing environmental conditions. But evolution doesn't give a damn about the relative quality of life we each have, or even if any particular one of us survives (after all, it is in evolution's interest that the unfit be eliminated), and it doesn't care if it's convenient or not for us to have a dozen or more children to raise and take care of at any given time.
Yet, because of the way we're designed, we possess an extremely powerful desire to mate with individuals who are attractive to us. So, assuming that having as much sex as possible, and just letting the babies come as they will, is unacceptable, there are only two solutions. One is to abstain from having sex except in those cases where procreation is the goal. And the other is to use our intelligence to manipulate nature in order to have sex while preventing (or greatly reducing) the possibility of procreation. In essence, thwarting evolution.
Now, I don't agree that the first solution is tenable. There might be some, who have a low enough interest in sex, that it would work. And for them, that's fine. But it's not going to work for everyone. And this is where people with certain religious opinions sometimes get on my nerve. They say that the presence or absence of pregnancy after any given session of intercourse is god's will, and that to interfere with that is unacceptable. Well, fie on them. This is one case where I have absolutely no problem 'playing God' (or even just mucking with his already fucked up plan).
But the point of this is that there is nothing wrong with pursuing sex for pleasure, absent (or detached) of any interest in procreation. We are intelligent and advanced enough as a species that we can afford to do this. Admitting, acknowledging, and pursuing our biological interest in sex while simultaneously doffing the incentive to procreate is neither immoral, irresponsible, nor unconscionable. And I would like to see less shaming of people with a decidedly 'prurient' interest in sex. There is nothing criminal or antisocial about enjoying a good lay, and it is not degenerative to explore or celebrate the virtues of sexual discovery and exploration in discussion or entertainment or the arts.