I don't think possession of revenge porn by third parties should be illegal. However, I do think a victim of revenge porn should have causes of action against the ex or whomever recorded and distributed it. In some countries, like Australia at least, recording and distributing revenge porn has resulted in claims in equity for breach of confidence - so something like that already works.
But prosecuting third parties for having it is asinine, IMO.
By this "moral" reasoning you're also fully supportive of revenge porn.