Re: Being overly complacent as Uke
First rule of Budo: protect yourself at all times. ALWAYS!
Aikido practise is inherently safe. When it is not, you are doing it wrong!
No one should make a point using pain/cause injury. Especially not the teacher. In case this happens do not train with that person, warn others about it or perhaps even leave!
In role of aite you allow tori to do the exercise, while protecting yourself at every step of the technique. It does not matter if tori is your teacher, an experienced student or novice. There is a risk that tori is too strong/too good for you to maintain control and you rely on your trust in tori. So know who you can trust, or do not train with them.
Accidents do happen, unfortunately, but they occur by chance not on purpose!