Skype social politics: I have a friend I want to block but can't.

It can be extremely hard, especially if you care about the person and/or if they are mentally/emotionally unbalanced. With the latter, many people probably fear antagonizing those with these type of conditions, especially if they are unpredictable.

I've have come to know quite a few people who seemed to have some type of mental/emotional/personality disorder. Some of them had disturbing/concerning behaviors. Making things more difficult, some of these people were my friends.

Some of them had positive qualities, but their negative qualities were sometimes extremely hard to predict.

These were type of people whom I would never want to get on their bedside…

Sometimes, coming face to face with a person who is displaying concerning behavior can be dangerous and frightening. Sometimes, it is best not to confront them outright.