Persactly Gorth.
So basically what this means (if we transplant it to KotOR) is that KotOR failed this kind of thing by making things too centered on a single action at the temple...
...though you "could" look at it that since "you" roleplay your character, any action you take should mirror the prior choices you made if you're really roleplaying.
If you master Lightside and then choose to flip to the dark for no real reason, then that's the fault of the player, not the game design.
Basically the way they connected the game to the ending (the temple "choice) more or less puts the fault on the player.
If you have a male character and were pure lightside and choose to follow Bastila to the darkside out of love(as someone else presented)... then you have that choice as a player... and that's your roleplayed choice.
That's hardly a fault of the game design, if anything I think that's a GOOD design to allow the player to make that roleplayed choice.
If someone makes the choice "just because", then that is the players fault in my opinion.
What they should have done (and would make more sense) is keep the "temple choice", but cut off dialogue options based on where you stood on the Light/Dark side meter... or at least alter how you'd make a full flip based on that. (i.e make you work for it if you really "want" to flip)
That way they could have kept the illusion that "all your choices" actually had an affect, while at the same time allowing this kind of "choose your path" freedom.