There are various definitions of atemi. I hope we can agree there are at least more than one, yes?
Though atemi, to you, is not about pain... it was not always so. In fact, Shioda Sensei has a very strict definition of atemi which was specifically geared TOWARD pain and potential k.o.'s. In his Aikido Shugyo book, he gives specific examples of leaving a class that O'Sensei had just been teaching ... and going out into the roughest parts of town to execute what he had just been studying. Shioda Sensei describes atemi usage that didn't just make contact, but put his opponents out of the fight upon one single hit!
SHOULD atemi be about pain alone? No. Absolutly not. But Aikido IS a martial art and I completely believe that proper use of atemi should be taught not just for training with other aikidoka, but also for the purpose of street fighting... god forbid we need to use it, but wouldn't you like to know it just in case?
Pain does not mean something is non-aiki.
That's my 2 cents.