Actually, I've never felt that I don't want to use skills or rather insights I acquired from my abusive therapists. Somehow, I have always been able to separate what I have gotten from the person in any relationship from the person himself. If something was working for me I was using it regardless of how that knowledge/understanding came to me and who helped me to get it.

Maybe, it's because I was more inclined to understand my own process when I was healing from abuse rather than to get mentally stuck on how horrible my abusers were and how horrible the whole system was etc. etc. I fully recognized the unfairness of what was done to me and I never suppressed my pain and anger, but, at the same time, I didn't want my thoughts to be hooked on the idea that I was just a victim of some sick individuals and some evil system and that was it. That felt utterly disempowering and depressing to me and I hate to stay in the place where I feel disempowered. Of course, I was a victim, but I wanted to understand which specific "sour spots" that I had my abusive therapists were able to exploit. In other words, I was more interested in understanding my own insecurities, unmet needs and wishful thinking that made me vulnerable in relationships in general and susceptible to exploitation so I could work on those areas so no one could ever exploit me again.

In other words, I was "selfishly" focused on myself. My well-being was more important to me than dwelling on how horrible my therapists were.

That doesn't mean that I suppressed or invalidated my pain and anger. I never suppress or invalidate any of my feelings. When they come I feel them fully because it helps me to release them out of my system. But once they go I don't go after them. I let them go and bring my focus back to my own life and my healing work. This "selfish" attitude allows me to use whatever works for me, including the skills I developed with the help of my abusive therapists, because, as you said correctly, no one is completely bad or completely good. We don't stay in any relationship, no matter how abusive it is unless there is something we are getting from it.

Another reason why I can use and appreciate what I've learned in therapy is because my healing work included looking at life from a bigger perspective and finding some spiritual purpose for every experience I've had in my life, whether harmful or not. This really helps to put a distance between what has happened and to look at it from a more detached perspective, and when you are able to look at things neutrally, you are in a better position to see what would work for you regardless of where you obtained those skills or knowledge. There have been many people in my life I couldn't stand, but I've learned a few useful things from all of them and I still use what I've learned.