...I can't recommend using any heavy water based detergent like simple green or purple power as it's rust waiting to attack instantly imo....
I didn't think Simple Green was a Detergent based cleaner, but I don't really know. It is supposed to be cut with water, so yes, it is safe to assume that most bottles you purchase have at least some water in them.
Simple Green is banned for aircraft because it is bad for aluminum. It has something to do with how alkaline its PH balance is. (AR-15's have aluminum receivers as well lots of other parts of the rifle, lots of pistols have aluminum frames)
Yet it is used in automotive that has lots of aluminum without any damage.
I think the difference you see here is, if the Simple Green is rinsed and flushed away, it won't won't damage the aluminum. Which is fine for Automotive, but the High Level of Systematic Safety of Aviation has banned it simply on the risk that it could seep in to places on all aluminum aircraft, and not get flushed away and thus do damage.
I use simply green all the time on all sorts of things in all sorts of applications, it is my Go To cleaner. I have never encountered it causing rust.... ....until recently, to degrease my slide and some of its parts for cerakoting, I immersed them in a tray of simple green, then got involved in other projects and forgot about them and let them soak for several days, instead of the hour or hours that is usually all that is necessary, I pull them out and find rust, not bad, but these are on coated treated parts... It looks like the few rust spots grew out of tiny unseeable by the human eye scratches in coating/treatment.
So this confirms what you say.... ....I'll only add its not as likely to cause rust as water, and won't if you flush it out or neutralize it after use, but it is possible...
People talk about using Hoppe's #9 to clean this or that or the entire weapon, I always point out, it is called Bore Solvent, not Firearm Cleaner. That doesn't mean you can't use it as a solvent as needed, this thread is a perfect example, it means you shouldn't make a habit of it to use it to clean everything all the time.
Since there are schools of thoughts that cleaning of firearms is different than everything else, it has been taken too far sometimes (especially from the Military). The military decided to dumb down cleaning to only using the same thing as the lubricant and protection. Which works, its just not as effective. They didn't want servicemen damaging the weapons experimenting with different ways of cleaning, and even good ways can damage the weapon if you do it right. While cleaning with the same lubricating oil, you can't screw it up.
When you do household cleaning, you never rinse or wipe away the solvents or nasty detergeant you use, you just leave lie on the surface? Of course not. People cleaning their car with detergents and soaps, or cleaning parts with solvents or degreasers, just leave those products on the paint or on the part? Of course not, you rinse them away or flush them out.
In my firearms cleaning box is the common cleaning and protecting products, like CLP, Bore Solvent, etc, it also has spray bottles of Simple Green, Denatured alcohol and even WD-40. I use the latter as appropriate, in fact the alcohol is for flushing out the simple green if I use it so it doesn't seep into nooks and crannies to remain and do damage. I don't use the Simple Green on my AR-15 because of all the aluminum, that could suffer worse damage than steel if any is left behind. WD-40, since its a mild solvent, to spot clean a stain, and to wipe down the exterior metal of firearms as corrosion protection.
So I use Simple Green on Firearms, as well as Denatured Alcohol and WD-40, sometimes even soap and water, along with all the other more common cleaning and lubricating/protecting products specifically for firearms.
BUT, AND THIS IS KEY, I use them appropriately and in a thought out systematic process. Not as a mindless, replacement of one for the other. Like the guy that decided simple green is such a good cleaner, he wipes down his firearms with it before putting them in the safe, Huh? Simple Green is NOT a substitute for gun oil, you're using it totally wrong!
I have been building two 80% frame pistols and cerakoting them. I have taken individual parts from a completely disassembled weapon and cleaned them in the sink with hot soapy water, then thoroughly dried them and treated them with a protectant oil product. It works very well, especially when you have parts covered in particles from filing. That doesn't mean a good way to clean a firearm, even field stripped, is in the sink with hot soapy water, no matter how well you dry it, water will get trapped in the assembled parts and rust will start.