I agree that preaching is often neither useful or effective. I guess that I think of it in a sort of Seidokan way. One of the interesting attitudes in Seidokan Aikido is that, often, it is possible to become more and more effective (technically) by doing less and less. However, unsurprisingly, the techniques stop working if you actually do nothing at all. Riding this razor edge of doing as little as possible and no less is, I think, the right place to be in terms of 'preaching.'
As far as coming to beliefs that I'm uncomfortable with: I guess that if I found myself at the head of a school where visitors were not welcomed or where advanced students gave the feeling that they did not value working with beginners, I would want to re-examine the message I was conveying. Here's another which is more personally relevant to me: I think that part of the 'philosophy' I see in Aikido regards concern and regard for your surroundings. Personally, I'm a bit of a slob and also don't put as much into the dojo as I should. I can easily see my students, if I have my own dojo, reflecting that. I'm sure preaching wouldn't make a difference, but I do think it would be time to examine what I thought might make a difference.