Any random civilian who designed an auto-loader system without Mechanicum approval would either be ignored or arrested and
they work in conjunction, if not watch over by, the Mechanicum
I don't remember giving the mechanicus this much free reign over our technology. The mechanicus should not have the ability to dictate what we design. If a single human life is lost above what is nessicary due to technophobia, then not good. I don't want them to have that much control, and I will vote to reign them in.
Edit: maybe in 40k, the mechanicus is entrenched enough to dissapear random citizens. However. Most world's have only been in contact for approximately 10 years, and the main common denominator would be thenus and lady serras. The mechanicus is fragmented and in it's early stages.
Manual reloading is fluff from 40k to show how far humanity has fallen. You say that turrets have powered aiming systems. A hypothetical chaos could hack the aiming systems, and cause friendly fire using Las weapons or plasma, two weapons that do not need to be reloaded. They just need a power feed to the core. They could do more damage than a manually loaded macrocannon.
Edit:imagine the havoc a chaos possessed replicator could get up to. We are passed the point of automation.
We are not signatories to the treaty of Olympus mons, and we have not given up everything to the mechanicus. The mechanicus plays second fiddle to us, and Thernus did not have techpriests when we grew up. They had sciences and engineering, and they currently have the most advanced science and engineering. Our home collages and design boards dictate our technology, not whatever drips and drabs the mechanicus sees fit to release to us mortals.
If we are letting the mechanicus drag us down, what are we getting out of the arrangement? We simply do not need them.
I do not believe that the mechanicus is a compelling enough faction for us to purposely hobble ourselves. Autoloaders are cold war tech.
I'm not asking for a completely automated turret. Have a bunch of crewmen aiming the gun, with lots of manual interlocks. Look at a modern tank turret. The Gunner selects which type of shell, the robot loads it far faster than a human, and seals the breach. Then the Gunner aims and fires, then the robot reloads.