I have studied in several schools for extended periods of time and have experienced those that preach absolute non resistance and those that preach strong resistancewhile training. Both, are hopeless, in my opinion. You need to train in-between most of the time, and from time to time, go to either extreme (not just a bit, but a lot at either extreme, then back tothe middle).
The middle road - very Buddhist in its wisdom. Not really sure what it is about Aikido and those that like to comment on it but it sure breeds a lot of extreme statements. I've seen this in the resistance game, but also speed vs static, name your concept.
Aiki in my view really reflects an increased sensitivity to your opponent. The ability to respond to their energy in a way that makes it your own. If there is no resistance during training then you can not experience that energy and learn to utilize it. Conversely if you are always working with hard resistance you will never learn to overcome that energy without an equal measure of force.