Hi d88 --
I agree with you on the basic impossibility of keeping everyone happy in a large, national organization.
Your response to Susan is fair (National PTA doesn't hide fact that it has political goals), but I think the rest of your long defense is a bit off the mark. Not because it's an inaccurate portrayal of what happens with Churches and Boy Scouts and Blockbuster, but because the typical local PTA and certainly the typical parent doesn't fit well into the analogy.
Let's use the Church/schism analogy. Lots of people join the Church. They decide that particular Church is the right one for them. The Church gets bigger and bigger. It gets harder and harder to keep all people happy. Finally, one particular disgruntled subset of the Church gets dissatisfied enough (and maybe has a charismatic leader/AC repairman

) and is large enough, so it breaks off to form own Church. Eventually, that subset -- if its successful -- will face same issues as original Church. I agree with your analysis on that.
But the average parent -- when his or her little Johnny gets to kindergarten or first grade -- joins the "parent group" at Johnny's school. If the school has a PTA, then the National PTA suddenly has one more "proud" member. If school has a PTO, then the parent is a "proud" PTO member. This parent doesn't even know the difference -- he or she was just trying to help out the school and show support and maybe chaperone a field trip and attend a few spaghetti suppers. (Important note: the chaperoning and the spaghetti-eating are
good things.) They didn't get involved because they believed in National PTA's mission and politics; they get involved because the flyer that came home said: "please send us $5."
So it's not like they got involved with National, then became dissatisfied (a la Martin Luther or the A/C repairman) and broke off. For most former PTA groups, the change came when they realized there was this whole political structure and political activity (that they were supporting with their dues and membership) that didn't fit with why their local group existed. It's not that they have a problem with the specific beliefs of National (in fact, if asked, most would probably agree with a lot of National's goals), it's that they separate their local school involvement from their political activism.
To extend the analogy, if they were Church members, they wouldn't be saying: "I don't believe in what this pastor is espousing -- I'm leaving." Instead, they'd be saying: "Church? How'd I get in Church? I thought this was the Elks club meeting."
Too many PTAers think that groups "going PTO" are somehow saying that PTA's beliefs are bad. That's not it. Most former PTAs are simply saying -- that's not the system that are parent group is all about.
Both options are fair opinions about what the "parent group experience" should be like. Both good options. Most groups (more each month) are opting out of the Church, not choosing a different Church.
I appreciate your input. This is an interesting discussion, and I think the most importnat crux of the PTO v PTA debate.
Tim