To Give or Not to Give – Privacy that Is

So, I have a 4 and a 1 year old, and a small dilemma regarding the big sister’s “need” for privacy. I am sure this is an issue we will revisit on this blog with greater seriousness in ten years, however, I am currently wondering about the validity of a child requesting privacy.
You know what I mean, she is hard at 4-yr.-0ld-work in her room — creating a My Little Pony corral or something — and in saunters her, newly walking, destructive one-year-old brother. She wails, “Mommmmy, can you get him out? I need privacy.” How she knows about the concept I have no idea, but that is beside my point right now. What I wrestle with is whether this is a legitimate request, or rather, whether this will ever be a legitimate request. I lean toward “no.” Isn’t privacy just an excuse for people to do immoral things? Perhaps it is innocent enough when she simply wants to create a project uninterrupted, but what kind of a premise am I establishing? Why can’t a person do whatever he/she needs to do in the light of day? I spent many a frustrating hour in college arguing against the “inherent right to privacy” supposedly found in the Constitution that abortion-advocates like to enlist as their legislative balast. If I don’t believe in the “right to privacy” outside my home, what does that mean here? Then I started thinking, Do I need “Mommy time” and isn’t that really a form of privacy? Or just sanity? Is that selfish?
Perhaps this rambled, but your thoughts on kiddie privacy and the ways in which you do or do not allow it in your homes would be much appreciated.