Ask HN: What's everyone's obsession with NDA's?

What's everyone's obsession with NDA's? As a freelance developer I am constantly running into people who absolutely insist that I must sign an NDA before we can either discuss their project.

My questions:

-Do you all run into this a lot?

-What do you say?

-Do you flat out refuse to sign and refuse to back down like me?

I think NDA's are arbitrary and unnecessary and I'm of the mind that if the person is so caught up on this they probably aren't worth working with.