Is it though? I mean, is it really a social construct.. or is it more inherent than that? Like a hardwired biological or evolutionary response? As far as I know animals don't engage sexually with the young, and the males generally don't attack the young males either.. until they reach maturity and start putting out scents etc.
Also if it wasn't hardwired, and incest wasn't hardwired too, then we'd probably have died off a long time ago from inbreeding surely?
I think any social construct has come about from observing something more inherent to our nature.
Just about all (predatory) insects, reptiles, avians, and mammals will attack young, and some non-predatory will also.
Young old and sick are generally the first targeted.
Primates are particualrly agressive towards young from other troupes.
Lions and other large cats will commit infanticide to prime the females of the pride of the newly defeated alpha to re-enter a fertile state.
Many animals however do not engage in sexual activity for the sake of pleasure though. This makes your point and alternatives to it rather moot though, as living under constant threat of danger, instinct makes animals wary of even releiving their bowels let alone coupling, which can be quite the immobilising activity for certain animals (read both the male and the recipient, particularly female). From the female perspective (even more moot as it's generally against the will of the receiving party - be they male or female - pregnancy in the wild is a serious issue and requires vast amounts of energy and effort).
Some animals also do engage in such activities as 'pedophelia' or more correctly, sexual interactions with young or not sexually mature individuals, but if it is not a human construct, and it is an inherrent or evolutionary response, then what does that truly mean ultimately, and for us in this time now?
Edit: solitary animals appear to work on a completely different set of behavior though, driven by calculatory logical and pure survivalist behavior. There's nobody to fall back on so every action you make must be calculated and weighed. Not that they are risk averse, but certain behaviors don't seem to appear very often because they don't have the liberty of 'choice' as such. It's literally your life on the line every step. There's also no social pressure to exert, and the female will often see a male as a threat outside of breeding, and males generally don't like other males outside of communal species, or in general.
Communal animals certainly show a much more diverse and interesting set of behavior because the dynamic is so much more diverse too. There is constant interaction. Pain is not a response but a stimulous, a tool, a weapon. Shock, awe, true affection, hatred, revenge, lust, jealousy... you could argue similar behaviors exist in solitary animals but i see them as more calculatory than underlain by emotion. But that's interpretation. Who really knows what the crocodile is thinking.
As Foreigner pointed out, possibly alluding to the Greeks with mentoring of young (males) including sexual acts - ie Spartans - or taking of young brides/young marriages, if the act its self is not a social human construct then the perception of it truly is. If a behavior is sanctioned by the masses then it becomes norm, and just the very fact that it is accepted lends strength to the act. It makes the group stronger because they agree on something.
Whether you think god smiles on you or doing X makes you stronger; or banding together to direct hatred at an action and strengthen the bond that dictates what is 'right'... the action becomes inconsequential and it's the response that matters in my opinion (for social animals).
As far as i'm concerned everything is fluid and false. We were burning or hanging witches maybe 400 years ago or so in the 'west' and similar practices still go on today. We thought the earth was flat and that we were never destined to achieve flight. Who is to say what is real, what is right? It all comes down to perception. And that perception (in a functioning society) no matter how another may perceive it or how horrific it is, will dictate whether the action its self is desirable, useful.
And to confuse my point further, there are sanctioned acts which are not to the benefit of the group. So what truly is right? Why are these behaviors there? Have we transcended logic, instinct or is our periodic failure just an extension of it? An evolution? Is there an end?