system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] Why did the Emperor discontinue the use of the highly-trained, effective clone army when the Galactic Empire was born? An army programmed to be loyal to him and trained from birth seems way more optimal than conscription and open recruitment of civilians.

And we all know how well the storm-troopers worked out...

Seems to me like continuing to use clones for his armies would be ideal.
gpt
The main reason is that the Emperor realised it was morally wrong to breed clones with short lifespans for the sole purpose of brainwashing them and sending them to war.

Just joking.

There's a few reasons. 

- Clones are extremely expensive to produce. You have to pay to breed them, pay to accelerate their growth, pay to equip them, and pay to train them. With non-clone Stormtroopers, you cut out the first two, which cuts out a lot of the cost. Sure, they're not as effective, but you already own the galaxy. Quantity is more important than quality at this point. It's also worth remembering that clones had significantly shorter lifespans, meaning you're not exactly getting a long time out of them. You can source directly from the Empire's trillions of citizens, cut most of the cost, and get more use out of them. 

- Having an entire army made up of clones makes them susceptible to sabotage, especially if you find the source. The clones had inhibitor chips that were added to make them completely compliant with things like Order 66. If they could be hacked/sabotaged, you could effectively reprogram the clones to turn on the Empire. Although volunteer soldiers would be more likely to individually defect, it's less of a problem than say if your whole clone army defects. This also covers the problem of if the technology was stolen, allowing other factions to breed clone armies of their own. 

- Having a military made of your own citizens would overall increase the stability of the Empire. People start to have a personal stake in the Empire's success, rather than if they were being protected by a clone army that existed purely to wage war.