What's your intention? To stab me with an imaginary knife? Those knives, I'm not so worried about.
Might they not stab at your mind?
As for wrist grabs, I've been teaching my daughter a variety of martial arts moves, and one of the first things I've taught her is the danger of letting someone get control of your wrist. Until I came to this site and saw this conversation, I had forgotten my (unfortunately brief) Aikido instruction had taught me what to do if someone grabs my wrist. I'll have to revisit that lesson some...
But from the perspective of someone who has trained primarily in other arts, I would say letting someone else control your wrist in a fight is a disaster. However, grabbing someone's wrist and controlling it are NOT the same thing. It is clearly possible for the one who has had their wrist grabbed to use that grip to control their attacker's wrist.