Why is the Turkish Government in my computer?
Per this list of "trusted root certificates in iOS 9" from Apple it seems this is just one of many of the trusted root authorities around the globe. While this is for iOS and not macOS, which you're asking about, I'd assume Apple would keep parity on these OS's.

If you were to untrust them I'd imagine some part of the internet (however small) may stop validating SSL certs on your machine.

Edit: Here's another list specific to macOS, straight from Apple.