I did this when I moved from brass to Blazer aluminum-cased ammo and have seen people do it with steel-cased ammo. Basically, for the savings of the non-brass case ammo, versus the damage, means that you save enough money to buy plenty of replacement parts. If you have shot enough to wear out the "gun" (extractor, bolt, barrel chamber, whatever), you have saved many times the amount of money to cover the replacement.
I remember the claim was that aluminum and/or steel ammo would wear out the extractor on my 1911 much faster, but buying Blazer was so much cheaper (while still being good enough for practice) that I could have purchased 1 extractors with every 1000 round case of ammo and still had money for lunch with the savings. Mind you, this was 20 years ago, but I bet the same math generally applies. I put over 80K rounds through one 1911 and wore out the rifling in 2 barrels, but extractors were not an issue.
This whole "should only be fired in guns designed for it" is nonsense.
I keep having these discussions with people who seems to think that design intent or "design for..." is somehow deterministic of the limits of what may be used, as if the gun was designed to only be shot with brass cased ammo so nothing else should be used. Never mind that most of the people making such claims have little or no insight into what the designer were designing for at the time or have knowledge of the designers' wishes (in this case) that only brass be used.
While I have lots of barrels and/or firearms that specifically state the cartridge or caliber to be used, absolutely none of my guns say anything about brass-cased ammo only.
Along these lines, I have seen countless 1911 discussions where folks talk about the condition the 1911 was designed to be carried in (versus the others which are wrong). I have read for Condition 1, 2, and 3 were all solely designed by John Fricking Mosely Browning to be carried in that manner (not the others), despite absolutely no historical documentation by Browning that any were specifically his idea of any one condition being the sole and only way in which he designed the gun to be carried.
I do have to wonder about guns that were designed with pretty much only steel cased ammo in mind as that was what was primarily available at the time, such as cold war AK47s. That was pretty much all Russia had a the time. Do people rant that the gun isn't designed for brass when people shoot brass-cased ammo from them?