I guess I just have higher hopes for people than you do.Usually when I ask a healer to DPS, they do it, if even for a little. Similarly, often when I advice tanks on how to pull (in leveling content) or DDs on better rotations (those BLMs...) they do at least try. And I know that if someone will give me advice on a job I'm not very familiar with, I will gladly accept it.
Like said, it's probably because it's not really a matter of discussion, because you aren't likely to find anyone to defend such a "play style" (unlike for non-DPS healers). A while ago I did start a thread about DDs who never LB, though, and there are many posts about these kind of DD and tank players in the DF stories thread.