Not sure why people are like that lol. I use water to rinse my gun after pouring cleaning solvent on it. With the exception of a wolf steel casing getting jammed today, never had a problem with my firearms.
Sadly, I'm currently learning about and dealing with rust issues myself. I think water can be damaging but it can also be fine depending exactly what you do. I shot my blued Sig P230 (not SL version) once, couple magazines only, and a tiny drizzle of rain fell on it. I wiped it off, put it back in the foam case, took it home, cleaned it thoroughly but didn't feel like oiling it, and the slide rusted up in spots exactly where the rain drizzled on it, one side only.
My guess is that a tiny bit of moisture got sucked up into the foam when I put the pistol in the case. So don't put a firearm that has been wet into a case, even if you've wiped it dry, unless you've let it sit outside for a few hours in dry weather to completely dry out. It probably also depends on the finish of the firearm. Blued or plain carbon steel is the easiest to rust I believe.
On the other hand, I recently purchased that crappy Birchwood Casey reblueing set to try to fix my once-badly-rusted katana (I only made it much worse). The instructions it comes with basically tell you to hose the firearm down with water after every step. So water can't exactly be a firearm destroyer, you just have to be careful what you do with it and make sure the water is totally dried off before storing the firearm.