Going form a handgun straight up to atomics is a bit of a step eh?
Also the thing, outlawed about atomics is not their destructive potential (There are far more worse things), the problem about them is their availability.
You do not need a law against virus bombs because there are not that much virus bombs in the hands of those that would be regulated by said law.
And all these other reasons you mentioned are because of one thing: Faith. The Cult Mechanicus has the monopoly on technology and is rather pissed if someone fabricates stuff. They do not ban guns because they kill people or hurt a bit but for they are against their believes, some of them make sense, some not so much.
There is a reason the Lasrifle is the gun of the imperium for it is always standardizes to a certain degree. Well, I do not want to be the guy that goes to the munitorium officer, trying to explain on a battlefield far from home, why he does use a non-sanctioned gun. Even less do I want to be the guy trying to get some assistance from an enginseer after he realized that the entire regiment is doing rather suspicious stuff.
IG Regiments can do a lot of stuff but openly and regularly carrying something around that is forbidden is rather difficult to explain with: "We are just some savages from a frontier world, intelligent enough to create some tech-heresy and stupid enough to sell it as our tithe back to the imperium."
Edited by FieserMoep, 24 May 2014 - 02:50 PM.