Originally posted by Hornet33 
Why not?? Soap and water won't hurt them. You wash your car right? Ever wash the engine of your car with soap and water? I do and that has more moving parts and electronics to boot than a firearm. Hell I've cleaned computer mother boards with soap and water and they worked just fine afterwards. 
Just have to make sure the parts are dry and then properly oiled on a firearm. 
 Cars often are rusty corroded things.  My guns never are rusty or corroded.
I typically tend to drive a car until the body is shot, and when it is just too rusty, I get rid of it.  I have several firearms approaching 40 years old,  not a spec of rust on any of them.  I have one firearm that is 70 years old.  No rust.  But then I don't use water on them, and if they get wet while hunting, it gets a complete dissassemble, clean and oil as soon as I get home.  If I anticipate moisture in the air while hunting, I slip a small can of oil and a few patches in my hunting jacket and oil the weapon during the hunt.
I have seen rusty guns.  I have never owned a rusty gun.
Bad comparison, cars to guns.
I never use WD40 on a firearm.  It dries off to much and leaves the weapon exposed.