Hi, moodycow. I have a long history with bpd, and I, too, have observed that we borderlines aren't the most popular patients in the psychiatric world.
Of course, as borderlines, we are sensitive to rejection and abandonment, anyway, so this generally negative reaction from folks who are supposed to be helping us doesn't help one bit.
However, by talking to therapists and observing my own history of interactions with them and other mental-health professionals, I have learned to understand why. First of all, yes, we can be very demanding and time-consuming. I used to call one of my therapists at least three times a week outside of our weekly sessions. I always thought I had good reasons to do so, but looking back, I am embarrassed about it. I even used to write her letters between our sessions! Gee, what if all her patients did that?
Second, our childhood history that led us to develop what's called a "borderline personality" also created a lot of rage in us. I did realize it was like I was a needy child whose mom wasn't giving me what I wanted, and I was mad about it. I would blow up at people very easily and even see slights that weren't there. And all these feelings can particularly be directed toward therapists and other professionals. They never know when we are going to light into them. And also we tend to just get mad and up and quit on them. Some of us can go from one therapist to another, never satisfied. Thus, it's frustrating for them to try to work with us.
That's what I have observed, anyway. I hope some of what I said has been helpful, since I can speak from wearing shoes like your own.