I'm asking on behalf of all of us that have seen the Babcock sex tape...

If they are having sex in their privacy and you are not watching them as a paid security employee or you are paid to watch whatever others do in the privacy of their homes but you use this information for voyeurism and stalking, then it's a sin.

You did not specify porn so the above applies. I assume you mean watching people have sex without the consent of the persons involved.