I think the actual crux of this issue is the choice of linguistic terminology used by adherents to both sides.
I actually further believe that despite semantics appearing the contrary we are all basically agreeing on 3 basic premises.
1. GW Fluff currently does not support the idea of canonical female marines. Again this refers to canonicity by GW.
2. Having said that, nothing is stopping GMs from personally modifying the game to suit their tastes. (despite the people going on about no longer 40k....bs is all I can say on that, its no less 40k than your 40k and any modifications you have made to the world, your modifications aren't canon and neither are the femme marines Equally, not canon.)
3. Though accepting of the fact that we "can" modify the game to allow for female marines, it is a divide in the fanbase and those who choose to delve into said realms should be prepared to deal with the derision such a change may cause in people we may otherwise agree with.
I have seen people against female marines say things with this at their heart, seen people for female marines say it, and I think the semantics of this issue are clouding our ability to speak to one another on the matter civilly.
Alexis
*smiles*
PS- There are no female marines in my games, I use a heretic order of S.O.B.s to fill that void, and it suits my needs, but I am completely nonplussed by the idea of female marines in other peoples' games.