I'm actually not going to use this as an opportunity to bag on the M&P. I'm not a big fan of the M&P, but its major flaw is its trigger, not its metallurgy. A slide cracking is just the result of using a Browning short recoil design. By camming the barrel down, it puts a lot of vertical force on the slide and frame rails. Just about any pistol these days can be made to break if the recoil spring isn't sufficiently strong enough to take the energy out of that blow.
That's why I'm so intrigued by rotating barrel designs like the Beretta Px4 and STI GP5/6. In those designs, all the force is applied directly back on the horizontal to the locking block & barrel lug. (Modulo leverage.) Even if either/or were to get peened or broken, replacing them would be easy and relatively cheap. That also applies to the Beretta 92, another design that doesn't use a Browning system, and is notorious for breaking locking lugs. Yes, it breaks, but fixing it is no big deal.
Just about anything will break with enough abuse. (Yes, even Glocks.) Ideally, what you want is a gun that fails in a predictable and cheap manner.