It does worry me that aikido can give people an exaggerated view of their capabilities when it comes to self defence. I think full-on randori is often the best way to break through these sorts of delusions, especially if something like a magic marker is used.
It is something I have been thinking about a lot since starting a dojo, where most new students put 'self-defence' at the top of their list of reasons to start. I think in future I will explain that "I am teaching a martial art, not self-defence. There is a significant difference, although one may contribute to your ability in the other."