I dont have any formal training in anthro or psyche, but I'm going to hazard an educated guess/give my opinion
What you're referring to is called a cooperation problem - in other words, what happens when that which is good/beneficial for society as a whole is not good for the individual. The classic example given of this is the free-rider.
Imagine a town that wants to build a mass transit system. Obviously, the fairest way to pay for this is to charge each rider according to their usage. But what if the fee was collected based on the honor system? Ie, nobody watching to see that you paid when you got on the bus, no turnstiles at the subway, everyone just went along on good faith, assuming that everyone would pay their fair share. Now, if ONE individual decides to shirk this responsibility and ride for free, there's no harm. He's such a small percentage of the overall ridership that his cost can easily be defrayed amongst the other riders. The problem comes in when 2, or 3 or 1,000 people all decide that they want to ride for free. The system isnt being supported and is unable to continue to operate.
Thus it's your assumption "social and instinctual sense would tell us they are crucial for spreading the populus of the species which seems like a conundrum if our main goal as a species is to procreate" that is faulty. Our instincts, while they do provide for teh survival and thriving of the species, are first and foremost concerned with OUR OWN survival. As in 'screw you, i wanna get mine.' Even tho the best thing for a group of hunting animals would be to spread the kill around equally, each wolf/lion/whatever wants his belly to be full more than he wants to make sure that all of his pack gets an equal share.
Same thing with societal individuals and women; even IF the best thing is to "share them" (for lack fo a better phrase) the prevailing mentality is and always will be "screw you, go share with somebody else."
EDIT to add - to sum it up in one sentence, if you're speaking about INSTINCTS and not reason, rationality, etc etc, the individual will put his own wants, desires, needs in front of the groups wants, desires, needs 99.9% of the time (and theres only a .1% chance of an individual sacrificing himself for the group instinctively and not rationally)