I think we all need our own privacy. But I think the difference is to what degree. I mean, the whole house can't be off limits when searching for paperwork. Where did you find it? In his personal diary or in a file in the file cabinet? I don't think we should look in our spouse's private diaries or personal effects just for the sake of looking there and being nosy, but at the same time, there shouldn't be anything your husband is hiding from you.
We all have our personal secrets. If your husband wants to keep some things private, say for instance his journals, then he needs to keep those things in a particular place and say this dresser drawer, or this night stand, or whatever, is off limits. Saying that everything he has is private is unacceptable in my opinion. You are married and what's his is yours and what's yours is his.
I know each couple's dynamic is different. I'm the keeper of all things financial in our house so this scenario would be the other way around for us. However, if my husband asked me to find the W2, I would have no problem letting him look for it himself. Of course, he wouldn't go and look in my journal for it. He'd look where we keep the tax paperwork.
I think it's ok to have some things be private. I always think of the Everybody Loves Raymond episode where Ray walks in on Debra when she's bleaching her peach fuzz (mustache). That was her "secret". Some people write about their fantasies in their journals or maybe things they do wrong, that don't have anything to do with their spouses, as a sort of confession or cleansing of the soul. I don't think a spouse needs to know about things like that. But in regards to this particular situation, me thinks your husband doth protest too much.
The request for privacy is reasonable, but the degree to which your husband is requesting it is unreasonable, at least in my opinion. :-)