Educated people tend to look down their noses at the accomplishments of the unlettered, and miss out on the value of both their accomplishments and the advantages of their learning processes. For centuries, they kept the "oral culture" under their thumbs by means of this disparagement.
What has become evident from the recent thread on harmonica education is that the unlettered, for their part, are no less prejudiced than their "educated" counterparts in their disdain for formal harmonica education. Perhaps, in part, as a backlash against the intolerance and poor teaching methods that have given formal education a bad name. (And perhaps because many of the people I am calling unlettered (the ones posting to this list) are in fact highly educated people who turn to the harmonica for a free-wheeling release from the pressure of their highly structured and demanding occupations and don't want their playground spoiled.)
At the same time, harmonica players wonder why the general level of harmonica playing ability is so low compared to other instruments (and why harmonica players are often not taken seriously by the public and especially by other musicians). Could it be that the existence of formal education for piano, guitar, saxophone, etc., means that higher standards have been created for these instruments, and that even those who hate standards and formal instruction have nontheless benefitted from them indirectly, due to sophisticated techniques and understanding passed to them by someone who got them from a formally educated musician?
To each his own road. You may wilt in the classroom but thrive in the poolhall. You may shine on the recital stage but feel lost and oppressed at a jam session. Go where you will flourish, but don't knock what doesn't personally suit you - it may be perfect for someone else - and, much more important, it may be an indirect source for much of what comes to you as an enrichment of your musical environment.
Given that, who could possibly be against harmonica education?