I haven't played through it all in 0.35. The last time I did play through Pure
it looked to be the way for Jenna to turn Karen back, as the things you could do to improve Karen's attitude required it.
Of course, the game isn't finished.
There are 4(.5), actually:
The main storyline, with the Pure variant being the (potential) .5. WIP.
Bar slut, which has an actual bad ending.
Drug whore, WIP.
Peitho slut trainer, WIP.
It's true that Jenna's corruption only goes one way, but that's true of (almost?) all of these games. That doesn't mean the developers can't have an interesting story or intriguing gameplay included for when the player avoids the corruption. Some even encourage multiple playthroughs via New Game+ modes that reset your corruption and/or experience so you can see the different paths without repeating too much grinding. (
Meltys Quest,
Ambrosia) A few have the corruption aspect woven deeply into the gameplay. (
Karryn's Prison)
I like seeing both parts of the story when the game (or visual novel) provides them; when done well it makes the whole more interesting. After all, if I just wanted porn stories, pictures, or animations there are much more efficient ways to get them than JRPGs and turn-based strategy games.