Because saiyans are nothing but stupid monkeys, right?
| Wandering, but not lost. | If people bring so much courage to this world...◊ |Having such confidence in your ability as to risk ending the world (And, indeed, letting 18 be absorbed against her will, which is sort of a dick thing to do even if she did break your arm) just so you can have a challenge is still pretty prideful and arrogant, though. He underestimated the strength boost Cell would get from his final form and overestimated his own limit.
You cannot firmly grasp the true form of Squidward's technique!
Well, now it's just semantics. Point is, Saiyans have a tendency to do dumb things because they're confident they'll win anyway/they want a challenge. Considering the species as a whole and their Blood Knight tendencies, it doesn't surprise me that King Cold would be aware of this.

Well, Trunks sort of proved he had no reason not to do it.
But Cold actually expecting that to work is astounding.
edited 28th Mar '13 7:00:07 AM by Saiga