It's probably far less than 5%. Most of the people who view porn sites are only there to view porn. After they have viewed it they aren't thinking straight and are unlikely to pursue intellectual questions like "what is Bitcoin".
Hmm.. I don't agree with your argument 100%. The guys will be there initially to view porn. But at least some of them will be noticing the fact that Bitcoin is a rapidly growing market, and investing in the BTC can make them filthy rich in the not too distant future. Most of the people who are addicted to porn, are also addicted to money.
