Personally I hate to think of the amount of steel cased ammo I've fed through my weapons. I've never noticed any excessive or funky wear from steel or suffered a broken extractor. Now, I'm not saying some weapon won't break something, but an extractor is, typically a wearing part, a consumable, it is subjected to severe abuse given it's location. I would guess if it were going to break with one type case, it was bound to break with another type of case, if given enough time. The steel case is typically a very mild soft steel, while it is harder than brass, it still has to be soft enough to flex to aid in trying to seal the chamber.
The biggest aspects I find with steel, is the steel wont expand when fired like brass allowing gases and soot to bypass the case, creating a dirty nasty chamber and other parts. Now this dirty nasty chamber/unburnt powder get mixed it any oil or even just on it's own could act as a lapping compound. It's a mild abrasive, over time, with the pressures generated, it could in effect wear something out. Along with the dirtiness, the coating used to prevent deterioration of the steel case, a.k.a. lacquer what have you, when it gets hot, it melts, trapping the filth/debris and eventually the fired cases. The hot pressurized gases, could act as a flame cutting torch, they may not cut deep, but each cracked case, bypass of hot gasses could remove very small micro amounts of chamber, like a microscopic cutting torch. This is where I think the issues with steel come from, dirty, sticky chambers, and the combined filth acting as a lapping compound on some weapons, and micro amounts of steel being cut away with cracked cases.
So I can see breaking an extractor, the case sticks in the chamber due to filth, if its a semi rifle, the gas system cycles after the shot, bolt flies back, pop goes the extractor, same on a bolt rifle or a handgun. if the case doesn't extract when fired, what is the first thing a hand gunner will do, try to cycle the slide, pop goes the extractor.
Some weapons were designed from the word go, while others, maybe not. Yea, the manual may say brass case ammo only, but like back in the day when auto manufactures said 3k oil changes
, it's to avoid warranty issues, comebacks, complaints and/or to keep from redesigning the parts of the auto or weapon. If you scare enough owners with the manual, with "brass only", I'm sure a majority will do it, their is smaller number who will use steel, saying screw the manual, and even smaller number, maybe a percent of a percent, might actually break something. So, the scare tactics by the manufacture obviously work, and only that percent of a percent are going to say "their junky product broke"
But, I have yet to wear any one weapon out to the point it just won't hit a barn wall from inside the barn.
Easy fix for me, typically, I believe in spare parts cache, so if and when I do break an extractor, at least I have a spare.
Just my opinion, yea, just like bungholes,
everyone has one and some just plain out stink.