So how do you stop sailors from tossing their crew off if they find it advantageous? That is the real question.

If you know beforehand that you will only have crew for so many days, apply for permission to change configuration before the event. I would not mind that.
In a local race where I know everybody I would not mind you changing configuration if your crew was scared/injuried/had to go either. If there is a RC/jury, apply for permission to swap crew or configuration and get out there.
Once there is something "important" up for grabs, we better play by the book, as that is the only way to minimize discontent in my opinion. Viewing it like that supports the claim that racing is a loosing game for everybody but the sole person/crew who wins (so we should focus on other stuff than racing).

What is it with racing you find fun? Is it the scoring, or measuring yourself up against others on the course? Like Phill said, you could go out and participate, but expect to be scored DSQ? (and possibly some grumbling about you being in the way when you have no business there).

I completely agree with you that this should be about fun, but we need a structure for racing to make sure it is reasonable fair.