Ok, this is entirely my opinion...
I think everyone in this world needs to learn to keep things in better perspective.
Is littering wrong? Well the obvious answer is yes, BUT...
Everyone who has their garters all tied up in knots about this single civilian "dumping" plastic bottles in the ocean with letters in them, should get a grip.
Spending such energy on such a tiny point is... pointless. To reuse an analogy I once heard, attacking this guy for littering it much like treating a blister on the foot of a terminally ill cancer patient.
If any of you are seriously against the pollution, your time will be better spent targeting something like cruise lines (http://www.surfrider.org/a-z/cruise.asp). I'm sure that you are all aware that every cruise ship saves it's garbage until it reaches international waters and then dumps it all. You couldn't fathom the amout of garbage they dump.
So in my opinion, though I do classify his actions as mildly inappropriate, I feel that he is more a romantic and less a criminal.
Even if he dropped 50 bottles a day into the ocean, until his last living day, he will not have pulluted as much as one cruise ship, on one cruise.
Oh, and by the way, I only chose cruise ships at random. I have no particular beef with cruise lines. I could have chosen a dozen things to use as examples. My primary point is that though this guys actions may be "wrong", they are minute when put beside the real pollution offenders. Pick your battles more wisely. This isn't even a skirmish.