* Waze is designed only to be used by a passenger. Any field that requires typing, etc. warns you if you're moving and makes you acknowledge that you are a passenger to continue.
* Waze has a hands-free capability where you can wave your hand in front of the phone and interact with Waze via voice. It actually works pretty well.
* The UI is designed with big buttons, so even if you choose to interact with Waze regularly, you can usually complete a road road report, etc. very quickly (1-2 seconds).
Regarding its "encouragement". I think alerts and the fact that they're available via audio as well reduces the risk. In the end, it's up the user to configure Waze according to how safe they want to be (which, hopefully is pretty safe).
(I'm a huge fan; I've been using Waze from the beginning. No attachment beyond that though)