Good advice given already.
you may want to add that the reason for non resistance is to save yourself from a lot of pain in the future. This often doesn't make sense to a beginner, as we do not apply techniques at full speed/power. If you are non resistant you can follow the technique you can avoid pain by making ukemi and therefore escape any pain. A stiff resistance will only lead to tears later on.
I admit it can be difficult when a newcomer is physically strong, to get them to fully understand this, particularly if they want to see if this aikido stuff is not just a bunch of wusses in skirts.
All part of the learning process Tomislav, you ended up fighting fire with fire, and got into the judo-ish stuff you mentioned. As a teacher you can't really afford to get into this type of contest without seriously questioning your own 'aikido'.
Aikido is non contention, don't fight what the other person wants, find out where they 'want' to go then take them there!