There's a very famous zenrin:
"Those who speak do not know,
those who know do not speak"
Unfortunately I suffer from a similar problem to yourself. I spend a lot of time talking about aikido, but I'm sure most of it doesn't get understood in the context in which I mean it. After a lengthy and overcomplicated explanaition of something down the bar one night a friend told me about his tai chi training, in which the instructor, when asked about something, just replied - "carrying on training and you will understand". And, strangely enough, he said after several years of training he did understand.
It made me realise that philosophising and talking about aikido is irrelevant without the training. Often beginners have the most questions, but the least experience with which to understand the answers. Now I try to give very brief explanaitions, in the hope that it abates their intellectual curiosity until they can understand what we're doing with their bodies.
This is related to a point I was thinking of recently - that people trained with Ueshiba (and many other top martial artists) because he had proven martial arts ability. One difficulty now is that people don't take everything you teach them without question because the instructor doesn't have a reputation for real self-defence. You have to explain the 'physics' etc behind it.
Other than being unethical and starting fights or encouraging challengers, is there any other way of giving students confidence in the utility of aikido?