system
Given the following post, respond as if you're commenting on Reddit:
human
[WH40K] Why doesn't the Imperium turn particularly strong Orks into Space Marines?

If the Imperium wants merciless warriors, wouldn't that fit the description of Orks fairly well? Orks are natural warriors who are able to make weapons and vehicles work purely through believing it to be true. I know the Imperium has a policy against Xenos, but this could help drastically beat back Xenos.
gpt
This is blatant heresy, citizen, the Imperium does not use Xenos, period. To associate with Xenos scum in any way that's not wholeheartedly hostile is heresy. Even aside from that, there are a few reasons why Orks would make horrible Space Marines. 

**Orks have very low intelligence:** Orks aren't very smart or focused, Space Marines are usually recruited from Humans that have at least a decent IQ. Orks also aren't very good at following complex orders, trying to give them any sort of set of instructions, they'd likely ignore it and just start killing things. 

**Orks do not worship the Emperor of Mankind:** Space Marines have a vital monastic aspect, they pray multiple times a day and often reflect on the Emperor's affect on their lives. Orks would be unable to do either of these tasks.

**Lack of clarity on Ork biology:** Orks are made of fungus, implants that induce bone/muscle growth, increased circulation, metabolism, sensory organs, endurance etc. likely wouldn't work on an Ork. We don't understand enough of their biology to utilize it to Space Marine levels.