On facebook one can certainly have more privacy, and people have all of their friends there, and can easily send undesirables off into pixel-land. I guess that "Delete a Contact" button is a bit of a magic wand.
On forums such as PT, one does not have that choice. And on PT (the same as all other open forums) you always get the troublemakers who just want to spew their garbage and cause arguments. Yes, we have three or four of them here who must thrive on that. I know of, and am in contact with, so many good members who have left PT because of them.
I'm not pointing any fingers here, we all have our up days and down days, but I can safely say there are some here who take much delight in being very rude.....and I believe that is 99% of why we here on PT, and others on other forums lose members. Where do these people go ??? Facebook !!! Where they are safe from such behaviour.
My two bobs worth.