Here's an idea, privacy first, ooooh anit we cool coders second. Privacy very much has to be the default, not google's cleverness or revenue stream.
All I can say is thank the non existent one that I don't use gmail for anything even vaguely important.
The only reason you don't have the same reaction to the location bar in your browser showing browser history is that you're used to it.
If you don't want email results to show up on your search page, just don't turn it on.
If that is true, why would you expect every site to assume you want privacy, when you chose to have customization by being logged in?