how about this situation - let's say you are a kindergarden teacher and one of your students gets really angry, saying he wants to hit you. are you going to fight a 6 year old that couldnt hurt you if he tried?
most rational people would probably take the attitude of "im at least 3 or 4 times this kid's age height and weight, i'd better not do anything to hurt him." one thing you probably wouldnt do is break his wrist or knock him unconcious.
could you do it? of course you could. would you? noooooo
aikido is an system that allow us to defuse a potentially violent situation with this point of view. if your skills are at a good level you wont need to beat the snot out of a 6 year old, some spaced out crackhead, a drunk or whoever it is that is attacking you.
no one's telling you not to use your aikido if you need it. does that mean you should act like jean claude van damme in some stupid 80's movie? i hope at 2nd kyu an aikidoka would act more sensibly than that.
now what if that pissed off 6 year old had a knife? or a gun?
it's not a black and white situation. if i'm face to face with an attacker and have ample opportunity to run, with no further danger to myself, why would i want to fight? it just makes the situation more complex than it needs to be. im going to take the simplest path to end the conflict.
if an attacker's punch has been thrown and is on it's way to my face, im gonna move.
if my back is to a cliff and when i irimi, he falls over the cliff, am i going to chase him down there and keep the fight going?