User blog comment:Roranoa zoro/Defeating Logia users without using Haki/@comment-10860731-20130707112056/@comment-10543621-20130710065837

It was more of the 'realisation of death' that paralysed Monet. Zoro basically showed Monet how terribly far apart their powers were and how easily Zoro could have killed her, had he chosen to use haki in that attack. The realisation that she could have easily died apparently stunned her.

And the killing intent method of paralysing only worked because Monet knew Zoro could have killed her with haki because he demonstrated his haki earlier with the cut on the face. So in other words, badass killing intent still wouldn't work if the user doesn't actually have the means to back up the killing intent (i,e. haki).