No question they are a great defense. The question is, do you want to defend very many, or any, greens that way? Statistically, I would say that less than 0.1% of players have the game to overcome a small, crowned green. Is it right to design a target that is essentially unachievable to 99.9% of golfers?
Recall that according to the USGA to have 2/3 of scratch golfers attain a green, it must have 14% of both depth and width of the approach shot yardage.....i.e. about 22 yards wide and deep for for a 150 yard approach shot. For handicap golfers, that would be 23 yards wide and 33 yards deep.
Dividing the entire green with a crown halves depth and perhaps width. Essentially, they are impossible to hold for almost all.
Frankly, I would design perhaps 1 or 2 crowned greens for an entire course, for variety, and only on short approach shots. I would put it on the scoredcard/yardage book/GPS as an homage to "Pinehurst style greens" or otherwise, golfers would just be plain pissed.......
As an alternative, doesn't a small raised tier on a larger green accomplish the same thing when the pin is placed there, but allow the ability to have the hole play more reasonably most of the time?