Unfortunately, and fortunately, celebrities give up a certain amount of right to privacy when they become public figures. In the life of a famous person, speculating about their lives and their work, even to the point of gossiping and telling untruths, can be done with a certain impunity, due to this clause 'public interest.'
If there is any legal defensibility to RPS stories, or RPF (real person fiction, not necessarily slash) it would be public interest. In exchange for the publicity they create and the living they make from publicity, the loss they suffer, while irritating and sometimes very humiliating, is to a certain extent both permissible and legal.
This is where ethics comes in. IF we apply the standards to Heath's life and to the suffering of his innocent family members, as well as his small daughter, as we do to our own, there are things we would never tolerate, and one of these things is people speculating about our sex lives and people we go to bed with. I believe that the reason we are talking about ethics here is that we are grappling with someone who has touched us all in some deep and emotional way, and to some ofus, we can no longer look on with what now feels like a prurient and selfish interest while others claim artistic right and freedom to do the same. I believe at base it is an ethics discussion.