Re: causing no (serious) harm
In my perception, aikido is definately not about walking away or avoiding a fight. It is about meeting a person and cooperating with them so you both get what you want. Timidity is not a method to prevent attack (nor is aggressiveness). I believe aikidoka should have confidence, honesty and the acceptance of the aggressors desire to attack or not, whatever the case may be.
I think if aikido is done well, in a practical situation, there will be less likelyhood of damage with less aggressive attacks since you are moving with less momentum/energy. However I know Ueshiba has been known to have said (to Shioda and Yamada I think) something like, 'in a real situation you have to finish it quickly...you know what I mean by finish it don't you?' (apologies for paraphrasing).
You have to think to yourself, what is the point of disabling/killing someone. If you believe there is a point to it, well, maybe you should do that. Personally, since I don't believe my life is any more valuable than another person's life, I think killing someone is no better (or worse) than you yourself being killed.