That was a textbook sack by Peppers, gotta hand it to him. My respect for that guy has always been kinda grudging though since I've seen both too many games where he's clearly the best guy out there and too many games where he doesn't really seem to give a crap.
Anyway, we'd run out of linemen if we had seasons that were as long as that of many other sports. Rugby is also very physical and has just as impressive tackles, but the blocking rules are a saving grace that keep it from being quite so bad, since the players are smaller in general and face less double and triple teams and less gang tackles (tackles are rather overrated as a source of injury in the NFL). In rugby, pretty much everyone is treated as a potential ball carrier and runs with the play until its eventual completion but gridiron doesn't really work like that. Hell, there's outright restrictions on who can pass the neutral zone after a forward pass-- the big guys would be stuck watching the play even if they were theoretically fast enough to keep up with it. That's why there is hyper specialization in the NFL with guys who weigh 270+ pounds and can't run a 40 yard dash in under 5 seconds are considered standard equipment on every team. And all they do is slam into each other and cut block every down. Autopsies have shown that several football players who died young (again, typically lineman, since they are very heavy men who are also very active) had brain damage on par with Alzheimer's patients, which probably explains why a few of them were homeless or considered unemployable despite being in their 40s or 50s. If anything the seasons should be a game or two shorter and practices should become more restricted. As it is the quality of play already suffers a fair bit due to the injury rates even if you toss out the ethical concerns.