Yeah, execution: AKA, the really, really evil and horrible way to run your business.
One thing, though - I'd make sure to create a loophole of some kind to let at least one girl still like you once you start dropping bodies left and right. People aren't logical, and even if you're the most despicable person in the world there can still be someone that truly loves you.
Maybe once a girl's PClove hits a certain threshold (i.e. the maximum), they're so in love with the PC - irrationally so - that even murder won't make them stray... but if her PClove is even one point below, suddenly she's terrified of you.
...it'd be an interesting way to encourage building a high PClove, come to think of it...
Also, I dig the idea of marrying your girls off, but instead of having it happen automatically, make it the player's 'responsibility' to find good husbands for his slaves. Every turn you have the option (set up like the walk in town button is) to meet a group of merchants/nobles/aristocrats who are in the market for mates; you select how many (if any! You might find them all to be scumbags and thus tell 'em no) you'd be willing to provide for. They then look through your roster and tell you which girls they want to marry (again, if any - I figure they'd each have certain criteria to try and match), and once again you have the
option to agree or not.
This way the player keeps as many options as possible, but it also adds an element of chance, in that rather than you selecting which girl to get rid of, it's them picking the girl, and you have to decide if you want to keep her or if you want to sell her off... but if you choose to sell her they offer top dollar (1.5x the girl's value?), so even if they want one of your favorite girls you might still find yourself tempted to sell.