Simon, your reply is both presumptuous and idiotic. By your immediate assumption and admonition, it reads rather more like the admission of guilt by an avid consumer of porn than any sort of informative answer to the question posed.
After all, are you really willing to let your co-workers, friends and family see your entire browsing history? Hmm, let's see... where you bank, your account numbers and balances for a start. Oh, you're researching what medical conditions? And ordering what sorts of medications? Maybe you're looking at job postings for other companies, or even within your own company. Grievance procedures from your union? Interesting. And this is just off the top of my head, with as little reference to my own privacy needs as possible.
Privacy matters, at least to me. There are far more interesting reasons to desire private browsing than something as mundane as porn.
And in case anyone really cares, there's an app called BrowseBetter that seems to fit the bill quite nicely.