Do you believe in space aliens?

A woman whose opinion I cared about asked me this question over ten years ago. Today I thought some more about why it was so hard for me to answer.

At the time, I had three responses available to me: yes, no and "insufficient data". The obvious answer was the third, and I wasn't able to say even that clearly.

Apparently, my brain has disjoint categories for "provable" and "things you take on faith". For whatever reason, I mentally file space aliens in the "provable" category. The question implies that space aliens belong in the other category and my brain just can't handle that.

I'm still trying to sort out why I find this question so hard to answer; feel free to contribute to the debate!