I think there is a middle position between the two that are being articulated and I feel bad for the original poster that the thread is devolving into "should there be monks in your world" instead of "tell me of the monks in your world."
The position I articulated, to reiterate, is that the monk is not a good fit in a campaign that is primarily based on Western mythic Europe. But there is no requirement that this be the basis of campaigns. So, instead of getting further into the argument that seems to be developing here, let me rephrase my original post in the form of suggestions:
1. Good campaign worlds can draw on multiple myth traditions provided they do so with intelligence and balance. If a GM wants to include both monks and Western archetypal classes (e.g. paladins), he should design a world that draws on both eastern and western myth rather than just importing the monk into an otherwise western story. There are a number of ways of doing this:
(a) running a Western-looking feudal campaign (ie. using Western names or tech.) that is actually based not on the European mythic past but instead on Japanese feudalism or Islamic chivalry .
(b) running a clash of civilizations type of campaign modeled after some variant of the crusades or the Mongol invasions of the 13th century.
(c) spending some time to create a unique fusion of European, Asian and brand new ideas that produces a totally different kind of world. But by spending time, I mean actually getting to know something about both European and non-European traditions so that these non-European features turn out to be better than window dressing.
2. GMs should be willing to modify the monk class in order to adapt it to the myth structure of the campaign. So, if you're anywhere west of the South China sea, ditch the shurikens and nunchaku. If you're anywhere west of the Arabian Sea, ditch the unarmed fighting style. If you're anywhere west of the Bosphorus, ditch the whole damned class.
So, to put this into practice, let's imagine modifying the monk class into the athlete of God of Middle Eastern Christianity:
(a) Make the monk a staff-wielder and have the stuff damage progress exactly and unarmed damage does now.
(b) Change the term "ki" to "merits."
(c) Grant wider weapon proficiency to compensate for the loss of special unarmed attacks.
A dervish, similarly, just need to have his ki changed to baraka, a special weapon or class thereof and a feat progression that points more effectively towards Whirlwind attack.
3. One might ask: why can't the monk class be modified into the European mendicant friar? My answer is: because the mendicant friar is already modeled in the form of an armourless cleric. The starting point for making a European monk is modifying the cleric class not modifying the monk class. About the only things I can think one would borrow from the monk for such a class are, possibly:
(a) Wisdom bonus to AC
(b) Lack of armour proficiency
I hope this helps in sending the discussion in a more constructive direction.