Holy Mother of Celestia, how did this topic grow this much while I was asleep? I'm beginning to understand in what kind of circle of Hell I ended into... (oh well, could have been worse: there still was that circle where souls were dipped up to their necks into a lake of shit and kept pleading each other to not cause a wave).
Still, now it feels horribly awkward to answer something that has been said
five pages ago

Also, I'd say it's natural to look diferently on someone you actualy had sex with. But I'm still a bit dazzled by what the difference is when someone says (I stress that word) they had sex with someone who isn't you. Does it make anyone go from "Pure inexperienced princess" to "old dirty hag" overnight? And there's more, you can tell?
For a brief moment of seriousness, it really is a male complex. Most people would deny it, or would justify it with some preposterous connection with the aesthetic canons from the French Romanticism in the XIX century (when you play the Baudelaire card you magically sound less of a pervert; funny, as he was a sick bastard...), but the fact is we are instinctively possessive, jealous dumbasses. We are jealous of the previous partners of our current one. There's no escape: some (hopefully most, but I wouldn't be so sure) men are smart enough to laugh at themselves for that and manage to keep such silliness at bay in their subconscious, but the spark, deep down, is always there.
It's nature, really, we may think of ourselves as bright, intelligent, whatever superior beings, but we are tied to those reproductive instincts that want only our DNA to be spread around and not the DNA of another one, and all that alpha male bullshit. The whole ludicrous value given to "virginity" originates from there, then it adapts differently depending on the current culture. It becomes supposedly important for males too, assumes religious significance, sparks aesthetics canons; since we are in an otaku forum, just think of the Geisha: the whole basis of such doll-like appearance was for women to appear pure, delicate, pristine, like a doll indeed, and that's nothing more than a convoluted mental process mirroring the idea of "virginity". Even though they were whores.
Men like to "desecrate" pure things as it makes them feel
dominant, and dominance over a woman calls to that spark deep down that wants them to be alpha males, to be the only ones granted the right to generate cubs.
Of course there are also opposing trends. Like many men liking big boobs and overall "experienced" looks in a mature woman as it tells their instincts those females show promise for being healthy mothers able to produce an equally healthy offspring. But to them I say: screw you. Baudelaire be my witness, you don't understand shit about beauty!

Which leads me to...
...But that part about fatherly insticts and...all, reminded me of 
... if you know who that is

Oh crap, you might have nailed it. Excel Saga was one of the very first anime I really got into before discovering the fansub world (as it was one of the very few to ever have been decently dubbed in my language)... Gojo might have been the primeval cause of it all, of my ailment. Next time I get obscenely drunk and the next day they tell me the girl I maked out with was seventeen years old, I know who to blame! *_*