Tom Doak said what I was thinking, and far better than I could.
Why do people arguing against the concept of defending par always start whining about it being difficult to make birdies? When the hell did we arrive at the expectation that birdies should be easy to come by? Next thing you know people will complain about small greens on par 5s because that makes it more difficult to hit the green in two!
I think this all goes back to the good old "hit it high and let it stick" mentality. This philosophy argues against firm or contoured greens because it is "unfair" if one hits a good shot straight for the pin which then fails to hold and bounds past the pin, or takes a slope and ends up away from the hole.
The better shotmaker is not one who can aim directly at the hole and hit it where he's aiming, with perhaps a bit of adjustment for the wind. It is one who can assess the situation and determine the proper spot to aim based on his skills and goals, along with other relevant conditions, and can stroke the ball in such a way as to maximize the likelihood that the ball either goes where he's aimed it or misses where he has determined is the best place to miss. The first is pure mechanics, the second is an art.
The best putter is not one who can can aim directly at the hole, or possibly a few inches to one side (since the modern architect fortunately can't yet create a completely flat green due to drainage needs) and hit it where he aims. It is one who can read the slopes and produce a stroke that produces the right combination of speed and line to allow the ball to drop in the hole, or if it misses miss where the easiest follow up putt can be made. Again, the first is pure mechanics, the second is an art.
Note that in both scenarios the best golfer requires a green that "defends par" to fully assess his skills and identify the player who has truly mastered the full range of skills including the "art" of golf, rather than a guy who has simply (OK its not THAT simple, but its far from the whole package) mastered the mechanics of alignment and contacting the ball with the club moving squarely to the target.
IMHO, the more you are against defending par the more you believe golfing skill is basically about mechanics, the less issue you have with defending par and can find few scenarios in golf you find truly "unfair" the more you believe golfing skill is basically about art. The mechanical guys think penal designs are OK, after all what's wrong with OB on both sides because a good golfer hits the ball down the middle. The artsy guys have a problem with penal designs, they want to see penalties imposed on the golfer by the difficulty of the situation he finds himself in after a bad shot, not three on the tee reloads.
There, let's see people start to tear this little treatise apart