For it protects everyone from the countless number of really stupid laws.
Someone made passing suggestion that sodomy is illegal in their state.
But I stopped and thought - how would anyone be able to catch anyone in the act?
Me and the big bootied bimbo that I brought back from the bar could just blame all the noise last night on having Animal Planet turned up too loud.
Lawrence v. Texas held that sodomy laws are unconstitutional wherein one has an expectation of privacy.
A state may have archaic laws on their books that forbid sodomy but they really can't enforce them.
Also nowhere in the constitution is a right to privacy even mentioned, but rather we get such a right from the law refers to as "the prenumbras" of our other constitutional rights.
Basically a good rule of thumb concerning privacy is that one has the right to privacy only when a "reasonable person ought to have a reasonable expectation to privacy.
Which is doublespeak for whenever there's a possibility that you might be seen by the general public, then you can no longer claim a right of privacy. To put this in practical terms, one can't go to a park and run around naked, then claim a right to privacy, because there's a good chance that someone from the public will see you. You can't even run around naked in your own home with the shades fully drawn and the windows open because again there's no expectation to privacy and someone from the general public might spot you even in your own home.
There's been quite a few SCOTUS cases covering the right to privacy and it gets really convoluted whenever you start talking about phone conversations, vehicle searches, and possible aerial survillence. Good reading material.