First of all, I respect the effort post. Nice to see that kind of energy around.
I fully agree with your proposed defining of the dangerous clause, as well as removing stunbaton/disabler from armed and dangerous clause. There's really no argument against this. There is never a situation where you need to lethal someone who stole a disabler. Not even lethals to slow them. As for defining dangerous as someone who killed a crewmember, this is also reasonable for reasons stated and would be a positive impact. Its what I've been following personally—the more crew killed and/or permakilled, the higher the equating response.
Now for the Stims/Implants/Bio-Chips
This is absolutely false. I've killed entire sec teams with 3 roundstart meth pills, because meth is that fucking effective. Now, there is a skill issue of course cause a few good harmbatons will bring me down. However, it is absolutely worth lethalling, and while yes security doesn't *have* to lethal, as charlie said, they were designed for such. When sec doesn't lethal an adrenal/meth user it should be considered a kindness, not a given. Just because its possible doesn't mean it should be expected in this circumstance. I object heavily to meth/adrenals being put off the lethal clause.
As a note, I am considering the fact that under your revised definitions, a meth user who kills an officer is now dangerous and able to be lethalled. I, however, support them being able to be lethalled before any such action takes place.
In conclusion, I feel there's a compromise that can be had of keeping adrenals/meth/stims clause the same, but changing the prior two points to your redesign.