I don't have to ask, I already know the answer for myself..:)
The friends I have , I do not judge nor base my friendship on their spirtual path or beliefs.
Same with family. I have a son who is a Baptist, because of what he believes should I not love him? No. I love my friends & family for all that the our, the differences included..:)
Absolutely. Why couldn't they? I am what many would consider a "black witch" but I have many Wiccan friends. They don't always agree with the work I do but we respect each other and that is what really counts.
One of my dearest and closest friends growing up was a "black witch", and we really didn't focus on who we were as witches, but simply enjoying each other's friendship (he was very attracted to my power). I was also friends with several of his friends, who were also black witches. They were great, very intense, and wonderful people to know. However, I did agree with the work they did because I totally understood why they were doing it.
The idea of black and white witchcraft has been circulating in new age circles for some time. Every witch knows about color and intent. If those around you are practicing aggressive and harmful magick, they suffer from a character imbalance and I would not trust them under any circumstances; if they could be honest, they would agree with me. They will probably use it against you if the opportunity arises. In the process of evolution they will cause turmoil and upheaval, and be a catalyst for growth and change, even if they themselves don't realize it... the fact that they are immature and socially out of touch doesn't render them useless; just don't be foolish in thinking of terms of black and white.
I don't necessairly see those who practice what most consider 'black' magic as having a character imbalance. We simply understand and embrace that we all have both a dark and a light side. It's about fully giving into our natures and deciding what is right and wrong for ourselves without the need for some external "rule" telling us "don't hurt anyone". We also realize that it is not always wrong to hurt someone through magic.
It's interesting that you used the word 'imbalance' in your post as I see those who practice black magic in some form as exceptionally balanced - possibly more so than some who practice only white. What is balance, after all, if not a well rounded understanding, acceptence, and expression of the entire self without denial or guilt?
So no, those who practice the darker arts aren't imbalanced in any way and they are no more dangerous to be friends with than the white light folk out there. We're not sitting there chomping at the bit waiting to strike the magic death blow at anyone we see. We don't bite..well, not very hard anyway :-)