For me it's about the couple rather than the sex they are, there's some couples I like to read about and others I don't.

That's definitely true for me, too! The problem in the Sherlock fandom is that basically every m/f couple is a rare pair, and there's just not enough fic to create any pairing-specific archives. If I go to a het-focused comm, I'll definitely be looking for a specific pair and not just "any old couple": the het-focus just narrows the field of fics I have to search through.

I definitely think that defining themselves as "Not-Slash" sends a bigger statement than if they defined themselves by what they do include. For that reason, I'm definitely requesting the removal of my fics!