system
Given the following post, respond as if you're commenting on Reddit:
human
[ATLA] Why didn't Zhao let Aang get killed when he captured Aang?

Zhao cites that the Avatar would just be reborn but why does that matter? Wouldn't killing the Avatar be the better strategy since the Fire Nation just needs to run out the clock until the comet arrives? And a newborn Avatar wouldn't be able to stop the Fire Nation. Plus total Fire Nation domination would make it easier to prevent the training of the new Avatar and there would be no airbending teachers.

This is in the episode Blue Spirit in season 1 where Zuko rescues Aang and gets shot by the archers.
gpt
At the time, there was no plan to genocide the world. They were still looking to control it.

Killing Aang had a lot of variables that could get in the way. The Norther Water Tribe was still standing strong so the next Avatar would have a 33% chance of either being born into a well fortified kingdom, a swamp or a small, still unconquered village. 

10-15 years with no Avatar to get in your way sounds pretty sweet but that's also 10-15 years of possibly not knowing the location of the guy who could potentially ruin everything. And the Avatar is more than just some person who can control all the elements, they're also a symbol for people to rally behind. 

Opposed to just keeping Aang locked up in a cell somewhere and not having to deal with the Avatar for a few decades. 

A bird in the hand is worth two in the bush, and all that.