Why were 17 and 18 evil in Trunks' timeline?

[Polyphase Avatron]

In the main timeline, 17 and 18 didn't even do anything evil except try to kill Goku and maybe rob a few people, otherwise they didn't even hurt anyone unless they were attacked first. Then later on they both reformed and became good.

But in Trunks' timeline they killed everyone. Why were they so different?

[dbgtFO]

They got bored
In any case I feel it's illogical for Kami to come to the conclusion that the androids in Trunks' timeline were inherently more evil than the ones in the main timeline.
The circumstances are wildly different between the timelines and who knows, maybe if they had ended up killing Goku and co. in the main timeline, they would eventually succumb to evil anyway just like in Trunks' timeline.

[Blade]

With Goku being already dead in Trunks' timeline, their primary objective was out of reach. There's no saying how they would have acted in the prime timeline had Goku not been alive, or had they been able to carry out their order of executing him.

[90sDBZ]

It wasn't just circumstances though. They spared the Z fighters and even suggested they take Senzu Beans, which is something their future counterparts would NEVER have done. In the future 18 killed children. In the present she has one of her own. I think it's because future Gero wanted to make them less human and more efficient killing machines so he did something to suppress their human empathy while at the same time making them a bit weaker as a downside.

[Kid Buu]

Its not like its ever explained why Vegeta and Freeza are evil either; they just are.

[DBZGTKOSDH]

The way I see it, Goku's death made Dr. Gero change his plans. He didn't use #19 (or he didn't even create him), he possibly destroyed #16 (or #17 & #18 destroyed him along with the lab), and he made modifications on #17 & #18 (he made them more evil, but suppressed their powers) when he decided to unleash them to attack instead of #19 & himself.

[rereboy]

In the main timeline, 17 and 18 didn't even do anything evil except try to kill Goku and maybe rob a few people, otherwise they didn't even hurt anyone unless they were attacked first. Then later on they both reformed and became good.

But in Trunks' timeline they killed everyone. Why were they so different?

I think that they are just the ones in the present, bored and over-powered, but since in the future they had been doing whatever they want and killing for a long time, they eventually became more twisted.

[FoolsGil]

In the apocalypse future Gero completed his work on 17 and 18, as in 100%. Being evil, they kill him and everyone else.

Trunks and Cell screw up the timeline, causing a butterfly effect---

Because of said effect, In the main timeline Gero doesn't complete his work on 17 and 18, decides to work on 19 and himself to become 20 instead. When he does release 17 and 18, they are not 100% completed, and thus more punk kids than evil.

[Super Saiyan Turlast x4]

I like the idea of Gero building the Future Androids for the purpose of world domination. I believe Future #17 says this in the Anime as well.

[roscaifed]

In the main timeline they are evil, maybe 17 more than 18 though. Even though this is filler, 18 goes into a clothes store and tries on clothes. She decides to spare the shop keeper because he was so complementary to her, which implies that she would usually just kill. 17 decides to blow the shop up anyway.

[ErikB]

In the main timeline they are evil, maybe 17 more than 18 though. Even though this is filler, 18 goes into a clothes store and tries on clothes. She decides to spare the shop keeper because he was so complementary to her, which implies that she would usually just kill. 17 decides to blow the shop up anyway.

That's a scene in the Trunks special; it's part of Future Trunks's timeline.

[roscaifed]

Damn you're right, the scene in the main series was the shop keeper calling the police

[Deep Thought]

I always liked the theory of 17 and 18's evil being a result of Goku's actions in Future Trunks' timeline. More specifically, while Goku killed Freeza and King Cold immediately, he spared the henchmen and let them go. The henchmen then wrought havoc on several cities and pre-cyborg 17 and 18 saw their parents get murdered in front of them by one of the henchmen. The Z-fighters clean up the rogue henchmen sometime later but by then the damage is done, and 17 and 18 are abducted by Gero, as per course. I forgot if this idea was stated in a guidebook or interview or if its' purely fan invention, but I like it. It seems like something Goku would do and it's a solid explanation as to why 17 and 18 would be so detached and uncaring from the rest of humanity, because they lost all that mattered to them.

[dbgtFO]

I really doubt Vegeta and Piccolo would go along with sparing them.

[Cursed Lemon]

I definitely think that being so preoccupied in the current timeline makes the difference. Sense of purpose does a lot for someone's morality.

[TenshiGokuu]

because goku already died prior to that time and doctor Gero decided to target the humans and make androids hate them so he can conquer the world, even the current 17 and 18 after killing Gero, didnt dropped their orders that they had to kill goku. so then even in the future timeline the wouldnt drop their orders to destroy the humanity

[Rocketman]

I think there was no difference in their histories or designs.

The difference was, the Z fighters weren't prepared, so they didn't have any senzu ready.

[DBZAOTA482]

Its not like its ever explained why Vegeta and Freeza are evil either; they just are.

Vegeta is the prince of a warrior race that is barbaric by nature so he has an exaggerated view on how saiyans should be like, and Freeza is a spoiled brat with lots of power.

[Polyphase Avatron]

I don't buy the "they just got bored" excuse, I mean 17 contributed energy to the genki dama to defeat Buu and before that lived as a law-abiding citizen apparently and 18 became a Z senshi, can you see any of the other Z-senshi (even Piccolo, who used to be evil) deciding to randomly kill everyone just because they got bored and there was no one around to stop them? I mean it wasn't hinted that it was something that they took a while to start doing, they attacked at the same time 19 and 20 did in the main timeline and kept killing the whole time.

[TheDevilsCorpse]

They got bored (no goal), had no moral guidance (16) and were unopposed in terms of power (everything else in the Cell Arc).

In the main timeline, shortly after 17 and 18 are released, the heroes catch up to them in terms of power. By the end of the arc, just a few days later, their power is basically like an ant to Gohan, Vegeta and Trunks. If they got out of line, they could be killed. The ones in Trunks' timeline didn't have that fear. They were released and didn't have a true goal with Gokū dead. I imagine that similar to the main models, they would have started by having fun and, without 16 there to ground them back into humanity, things grow exponentially from there as they eventually needed bigger and more exciting "games" to satisfy them. Fighting with the Z Warriors probably exacerbated the situation, as that would be the most fun they could have at the time and all their actions afterward tried to recapture that feeling.