There are too many "why not?" responses to consider them all rhetorical.

1) It's inconvenient.
2) It's a psychological burden to have to consider theft at every turn.

Yes, of course it's even more inconvenient to have the dinghy stolen. However, the actual probability of the dinghy being stolen also figures into this calculation. Personally, a discussion of the actual prevalence of dinghy theft and it's consequences is of more value than a blanket "why not?" applied to every possible precaution.