system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek]In multiple shows, transporters make extra people. Without extra mass. Which means that the magic box somehow converts energy into mass. So why don't civilizations like the Dominion use transporters to make tons of soldiers on demand instead of training them?

There are cultural reasons that many civilizations would not do this, but there are lots that would. We don't know exactly how a transpoter works, but on so many occasions it ends up making extra people. So it can't simply be moving atoms from location A to location B.  Any in niverse source that says that, must be lying or wrong. Probably just lying, since the other implication is the transporter might be a murder box and then civilizations like the Federation would not be comfortable using it.
gpt
Because in literally every instance of it happening it was a massive fluke with very special non repeatable circumstances. 

The next best thing is to grow your own troops. It's reliable, controllable, and gives you all the ketracel white you can bury your face in.