To me this is simple. If you buy a nice car, you want to drive the nice car, you don't put a limit on your nice car, and not take it when you want to drive the nice car. It's going to get wear and tear and decrease in value. You don't do anything stupid with it, but you don't start walking to the grocery store just because you don't feel like driving it. Especially if your 5 games ahead in the NL East.
If you buy a nice house, you don't fear living in it for giving it wear and tear, that's part of the deal when you buy it. What value is the house to buy it, then put a fence up and say "nope, not going to live there, can't risk breaking something, must live somewhere else".
Unleash the Beast
The point is, this kid is in his early prime. His elbow is fragile, he's already had Tommy John surgery. But you can't fear that, if he's inclined to have elbow problems, stopping at 160 innings isn't going to help. He's going to be the next Mark Prior no matter what you do. And in that case, you should strike while the iron is hot. These days MLB team windows are narrow, if you don't win one year, the other teams will get enough free agents to make sure you don't contend the next (ask the Rays, Phillies, Giants, White Sox, etc.). I can't IMAGINE being a fan of this team then being told "winning this year isn't important, winning next year and the next (without any context to status) takes precedence."
It doesn't work that way. Win now. Be smart, don't let him labor too much. But let the boy pitch, he's good, your team is good, and the fans deserve it.