Kutcher posted his defense on his own blog. Here's what Ashton has to say:
I don't smoke marijuana and any statement to the contrary is a lie. I simply feel that Michael Phelps is entitled to his privacy. The kid made a mistake (he is only human) and anyone who has been in the public eye knows the magnification of minor missteps can be blown way out of proportion. Yes he is a role model and a great one at that. But I'm sure that in his lapse of judgment he wasn't thinking, "boy I hope the whole world can see this so that kids everywhere can copy me." And truth be told, if they went out and trained and worked as hard as he has to reach the great heights of success in their careers I wouldn't hammer them about a slip up either. And in kind I would like to retract any negative statement that I made about the kid who published the pic. I'm sure he/she wasn't in a sober head space while taking it or publishing it for that matter (you are the company you keep). I leave perfection to the creator of this great universe and wouldn't assume that duty on any human being.
BTW: That photo that you see above is neither Phelps nor Kutcher. It's Demi Moore bending over in a white bikini. Ashton took the photo and posted it on his Twitter page. Demi's reaction?
"He is such a sneak and while I was steaming his suit too!"