I believe SEO is blackhat. There's no whitehat and blackhat because it's SEO not RACISM. I know my personal experience from blackhat forums that everyone uses the same techniques. Whatever guidelines "Whitehat" follows "Blackhat" follows the same. Hell they tend to follow guidelines more strictly than Whitehat pros. If you think keyword stuffing and stuff like that is Blackhat then please update your dictionary because it's called spamming. And whether you believe it or not all agencies do Blackhat SEO one way or another because that drive results it's just that no one wants to exploit their reputation
I somehow agree with babloodabloo here. But I want to tell you that if you are doing SEO for your own website you choose ethical tasks for getting a reputation that never drops that is a genuine SEO or whitehat BUT when you're doing it for your client's business, all you do is getting rank in the search engines no matter how. That's what I called a black hat SEO.
I agree that techniques used are same in both, but in WhiteHat you only focus on your target audience, possible clients, Higher ROI and all of those tactics in ethical way or you can say "An Optimization" and in BlackHat you dont care about target audience all you care about back-link count so that you get ranking or Clicks or Impressions.
After all only a "BlackHat" knows how to do "WhiteHat"!