I have casually dated a BDP chick for a fair amount of time. And I wasn't f**ked over by the experience. But here is the issue:
Casually dating a REAL BPD chick involves the same amount of effort involved in a real relationship with a normal chick. It's not as simple as "I call BPD chick at 2am, she comes by, we screw, and she goes home."
Even if it's just casual, even if it's just for the sex, you're dealing with mood swings, attention wh0ring, the anger that comes when you don't respond to their attention wh0ring, drunken drama, attempts at creating jealousy.
It just makes you realize "Okay, I saw this girl naked. I banged her 30 different ways. I've accomplished everything I wanted to with this girl. It's not worth dealing with this sh!t over an extended period of time."
What I notice is this: Even when you ignore her BPD attempts at drama, all the chick will do is ESCALATE the drama in an attempt to get some kind of reaction. You're not going to tame the girl. And ignoring her doesn't work, and sometimes makes things worse. So you end up putting yourself in a "casual relationship" with a ticking time bomb.