This is indeed quite intriguing. I might try to engage a couple of the priests back home on this sort of discussion. As I recall one's largely more conservative than any else I've met (the archbishop included) whilst the other was quite happy with the idea that The Creator (whom we, at the time being a catholic, term God in at least part of our belief system) could happily be viewed as a three-headed dragon...it didn't really have any significance or relevance to the importance of 'the message'.
They always were interesting characters for debate; getting to the heart of religious arguments can be quite enlightening. Looking at the
Humanae Vitae line of reasoning (as well as some curious ideas like those parodied by Monty Python's "Every Sperm is Sacred!" song), it draws my reasoning back towards ID2004 Science Ethics.
That is the idea that drawing any sort of line between 'life' and 'can be sacrificed, not important' (i.e. when abortion is permitted, when it isn't) can be brought back before even conception when one considers that a combination of sperm and egg, even not inside a person but simply kept (safely) in containment elsewhere could be turned into a person. One might then argue that, if the potential for life is important as is being alive (to say that they are both Important and not ranked hierarchically at this point), then you run into some serious difficulties (and, for me, a whole big logical mess).
My objection at the time (still being catholic) was that conception was the least arbitrary position. Placing abortion deadlines after conception was (excluding obvious time-dependent objections), to me, just as arbitrary as forbidding masturbation etc.
My think, albeit surely becoming lost in a miasma of flawed logic, was then that a seriously mindful view with respect to preserving, maximising and keeping the potential for human life etc was simply to extract the sperm and eggs from
everyone as soon as it's feasible to remove them!
(and then only ever
create children and human life when it is feasible to do so, but never killing off unwanted sperms and eggs)
This, in a manner, would also protect us from the inherent sin that is simply 'life wasted' because of how nature works (one might even tie this sort of thing in, ethically if not realistically, with original sin and being expelled from paradise etc).
In essence, the most ethical move would be to entirely divorce sexual intercourse and reproduction. Thus the only 'sin', problem or other sort of dilemma is only to do with that of sexual intercourse, the argument from preserving life (and so forth) would be...won.
As I said: miasma of bad logic. But I did find it a particularly compelling line of thought to browse through!
Anyway, as it stands now I'm an apostate, probably due to the application of occam's razor to the above problem. Which is: the incidental loss of sperm and eggs (and all the possible combinations that can't be followed once you select one sperm and one egg, even alternatively a whole bundle to 'fight it out', and they're locked into their 'one life' [excluding twins, triplets etc]) doesn't appear to be an tangible (and, if you'll forgive the rather inflammatory phrasing) real-world issue. It's a fabrication, an affectation that really has no place being added into (my opinion of my idea of) ethics!
Now I'm a happy apostate.

[hr]
"There is only ever one truth. Things are always black or white, there's no such thing as a shade of grey. If you think that something is a shade of grey it simply means that you don't fully understand the situation. The truth is narrow and the path of the pursuit of truth is similarly narrow."
Also, some years later:
"here we are arguing about a few uppity troublemakers with a bee in their bonnet and a conspiracy theory."