I wouldn't unfriend someone who technically disagreed with me but yes I have un friended people who I feel are too different from me. i.e a friend whose partner used to beat her up all the time. I told her time and time again to leave him, I offered her help numerous times ect but after 4 years I got to the point where I didn't want to be around her or him anymore. I also have very strong opinions on drugs so have unfriended someone who let someone else bring them into my house.
I would definately unfriend someone who told me that they were terminating based on gender preference. Seriously why would you tell someone that and expect them to support you.
Regarding facebook I actually had about 150 *friends* I culled some , then some more and now I have 47. Seriously most of these people are not your friends and if you saw them in the street they wouldn't even bother to say hello.