Dear friend,
My opinion only . Watching PORN to many is more like nothing wrong done at all as they are not hurting anyone directly .Do you know why its sin in God's view ?
hypothetically , think of family members who are close to you . ( Mom, Sister, Daughter, Son etc..)
Will anyone able to watch PORN if any of their close family members are involved. I would say 99% will definitely say NO to it as they love them and cant see them in that condition .
God treat every human being as his son, daughter and thats reason its Sin to watch PORN .