It is true the possibility exists. Since the replicants were whatever Tyrel et. al. made them, then the question is “why did they make him not nice?”
I’m in this same corner. I do find the possibility that JF contributed his weakened genetics into the replicants a nice twist. I had always assumed he was just bragging a bit on his part in their creation, just like his toys. The fact that we don’t see the aging happening in the replicants, nor see any external effects before Roy’s bit with the nail through the fist, makes it hard for me to read as much into JF’s line about “some of me in you.” The spacing in time between the JF line and Roy’s sudden deterioration made it hard to connect for me, but it’s nice to have that pointed out after the fact – after many viewings of the movie.
My original take, before all the possibilities presented in this thread, was that Roy may have felt a bit of sympathy for JF’s decrepitude and did a mercy killing on him. It had been Pris who was JF’s buddy, not Roy. Roy’s only shared moments with JF had been the chess game and I felt that was just a prelude to doing JF in, whether or not Roy got any satisfaction from Tyrell. I gathered that Roy had feelings for “his own” but not for his creators.
The redemption factor, plus the beauty of his death speech, makes Roy the most intriguing character for me. I have yet to see that scene without choiking up.
JF bolted (or at least tried to) after Roy squished Tyrell, so I kinda doubt he was asking to be put out of his misery.
Well, no. Not in so many words anyway. Besides, regardless of how JF saw Roy, I thought Roy felt some sympathy for JF. Kinda like putting a pet out of its misery, whether the pet feels any misery or not. No doubt JF wasn’t ready to go, but that wasn’t Roy’s issue. He was ready for JF to go. So he went.
Roy was a combat model, “optimum self-sufficiency.” Zhora was part of a kick-murder squad. Pris was a basic pleasure model, but obviously one you don’t want to piss off.
Anyway, if they weren’t nice, it’s because they were designed to not be particularly nice. Plus, they were only three to four years old. Emotionally, they didn’t have a lot of socialization skills to rely on. You train a three year old to kill, it’s not going to differentiate much between a “good” killing and a “bad” murder.
Begging the question that has haunted me for years: just what the hell is a “kick-murder squad” anyway? Do they kick you to death? Do they get their kicks out of it? Or was it just meant to sound cool?
I’ve always wondered.
Smithers: I discussed this with our lawyers and they consider it murder.
Burns: Damn their oily hides!
“Kick-murder” kinda baffled me, too. Sounds cool, though. I’m more annoyed by the lack of explanation for the missing sixth replicant.
Anyhoo, I know a lot of fans rebelled at the so-called “happy ending”, in which Deckard’s voice-over casually announced that Rachel had no termination date. This never struck me as especially contrived, since the whole point of the four-year limit was to eliminate replicants just as they were starting to develop emotional responses (given what happens in the movie, I’d say a three-year, eleven-month lifespan is probably a good idea). Since Rachel already has emotional responses, built on the formative childhood memories of a human woman presumably chosen for her emotional stability, it isn’t necessary for Rachel to drop dead the next time February 29th comes around.
I think it just sounded cool. It evokes a mental image of a very cold-blooded, vicious death squad who can kill with nothing more than their hands & feet (imagine in this future there are lots of weapon detectors everywhere off-world). Later in the movie when we see Pris doing that back hand-spring attack on Deckard - and she’s just a pleasure model - it’s easy to imagine how horrible an actual kick-murder squad must be.
Well, if you’re going to beaten to death, it may as well be relatively pleasant and involve a hot babe doing backflips.

Hey, I hate my boss. After I punch him out, I might stop to kick one of his lackies in the nuts on my way out.
My point exactly: Tyrel didn’t make them nice, though he could have. Nice people can be trained to kill, the military does it all the time. Tyrel fucked up.
It’s been awhile since I’ve seen the movie, but maybe “kick murder” wasn’t literal? Like if he’d said “some hot shit assassination squad,” it’d mean that the killers are “elite,” not that they use some horrible colonic flamethrower attack method.
And…JF was trying to run when Roy killed him, right? Maybe if Roy wasn’t especially worried about him being a witness, JF calling security or pulling a fire alarm might cause more trouble than he wanted to deal with at the time. (Badass replicant or not, having to fight his way out of a building filled with corporate security and surrounded by police wouldn’t have been fun.)
Well, actually I think Tyrell was (in his own God-conmplex sort of way) trying to do just what you propose. He liked making people, not machines. The government/s, however, wanted controllable slaves. And even in Blade Runner, who’se to say that putting in instinctual nice-ness works out?
We don’t know that for sure. Tyrel could make them strong and he could make them intelligent, but he was still working on the “nice” part. That’s what Rachel’s memory implants were for.
Without those critical growing up years, humans er… I mean replicants tend to be kinda sociopathic, don’t they?
I’m getting an image of Rockettes in hobnailed jackboots . . .