STELLA: We've become a race of peeping Toms. What people ought to do is get outside their own house and look in for a change. Yes, sir. How's that for a bit of homespun philosophy?
The plainspoken and practical Stella knows something bad when she sees it and has no qualms about letting Jeff know it. Jeff knows that it's not okay to spy on the neighbors, but he does it anyway—likely because he sees it as a largely harmless vice.
JEFF: She's like a queen bee with her pick of the drones.
LISA: I'd say she's doing a woman's hardest job: juggling wolves.
Jeff is pretty happy to condemn Miss Torso for her perceived sins, even taking a kind of sardonic glee in it. Lisa brings a woman's perspective to the equation, and suddenly the moral burden shifts from Miss Torso to her suitors.
JEFF: I wonder if it is ethical to watch a man with binoculars and a long-focus lens. Do you, do you suppose it's ethical even if you prove that he didn't commit a crime?
LISA: I'm not much on rear-window ethics.
JEFF: Of course, they can do the same thing to me. Watch me like a bug under a glass if they want to.
It's not ethical—though it's not as bad as murder—but Jeff is also aware that it's a two-way street. Does that make it right?
STELLA: What'll you do if one of them catches you?
JEFF: Depends on which one.
So, morality is flexible, right? It's okay to watch if whomever you're watching is a nice guy who won't pummel you when he finds out.
LISA: Sitting around, looking out a window to kill time is one thing, but doing it the way you are with, with binoculars, and with wild opinions about every little movement you see is … is, is diseased!
JEFF: Do you think I consider this recreation?
LISA: I don't know what you consider it—but if you don't stop it, I'm getting out of here.
JEFF: You'd better before you catch the disease!
Rear Window doesn't totally condemn Jeff's voyeurism because it knows we all share it. Witness Lisa, aghast at her boyfriend's proclivities until she, too, becomes hooked on the sordid little drama unfolding before them. Ain't nobody's hands clean here.
DOYLE: Now, don't get me mad! Even a detective can't walk in anybody's apartment and search it. If I were ever caught in there, I'd lose my badge inside of 10 minutes!
JEFF: Just make sure you're not caught. If you find something, you've got a murderer, and nobody will care about a couple of house rules. If you find nothing, he's clear.
DOYLE: At the risk of sounding stuffy, Jeff, I'll remind you of the Constitution and the phrase "search warrant," issued by a judge who knows the Bill of Rights verbatim. He must ask for evidence.
Professionals are bound by laws and codes of ethics that laypersons don't have to worry about. It's morally questionable, but not illegal, for Jeff to take an unusually close interest in his neighbors' activities. Doyle, OTOH, can't just barge in to any apartment he wants just out of curiosity. Probable cause, etc. What a stickler.
LISA: Jeff, you know if someone came in here, they wouldn't believe what they'd see. You and me with long faces plunged into despair because we find out a man didn't kill his wife. We're two of the most frightening ghouls I've ever known.
At least Lisa and Jeff are aware of the moral implications of what they're doing. Of course, that reflection only lasts until new suspicions arise; then they're both back at their voyeurism with even more enthusiasm.
STELLA: Give her another minute. She's doing this for you!
This is a key reminder that, even though Lisa is engaged in technically illegal activity with Jeff—as well as putting herself in great danger—she's doing it for another person. Jeff seems to be doing it solely to fulfill his own curiosity.
JEFF: Lisa … I … I can't tell you how scared I was that you … you might …
LISA: Shut up. I'm all right.
Jeff realizes here how reckless he's been with this investigation and that his actions might have hurt someone he cared about. Not only was he invading his neighbors' privacy, but he was also endangering Lisa. We know from his racetrack accident that he's not a genius at considering the consequences of his actions. Isn't that the basis of morality?