In my opinion an Aikidoka should never atempt to cause injury on another person. Aikido techniques are dangerous, therefore should be used only in self-defense and even then with caution and self-control (with peace of mind) in order not to hurt your "opponent".
When training in Aikido I consider those that attack not as Aikidoka for that particular moment. And when I attack, I'm not an Aikidoka for the time being. I'm just providing my partner with the necessary impulse for him/her to try and defens him-/herself with an Aikido technique.
That is also why there are no attack technique in Aikido (at least the "version" im training in). Doing e.g. shomen-uchi for me means DEFENDING from a hand/blade/whatever trying to chop you up rather than trying to chop up someone.
I read once a statement of O Sensei, who claimed that even when you perform an Aikido technique you should be careful not to hurt the person who attacked you. I belive that says it all.
Finding the border-line between doing a successful technique and hurting your partner is what Aikido is all about (for me, at least).