If it were just "some guy," I would be inclined to agree with you and conclude that a fly-by-night troll dropped in to make the site look bad.
In the case of My.Barackobama.com, and MoveOn.org in 2006, it wasn't "some guy," nor was it even ten guys. It was literally dozens or more. Nor were they fly-by-night operatives; the point scores at MyBO showed many to be long-term participants. A Google search brings up more than 300 pages that talk about the "Israel Lobby," a term approved by an official campaign staffer (Emily). There are still more than 60 pages that come up under "Jewish Lobby," although I think they are now trying to sanitize their site by removing these.
If you do a Google search on barackobama.com for "McCain" and "Alzheimer's," you will find more than 300 pages that propagate this rumor, with no more foundation than McCain's age as a risk factor. This isn't "some guy" or even "a few guys," it's a pattern of behavior.
MoveOn.org tried exactly the same excuses unsuccessfully. MoveOn tried to blame Republican operatives while denying that it ever saw the hate speech. The only thing that saved MoveOn was its decision to finally close the Action Forum, and I am one of the people who made that happen.
Your argument (anonymous people are posting hate speech to slime Obama's site) could easily be turned around. How do we know Obama campaign staffers aren't posting the Alzheimer's stuff at MyBO and YouTube under pseudonyms to promote this rumor, thus allowing Obama to reap the benefits without taking the blame?
I'm already working on payback for that one by pointing out references that say cocaine use, to which Obama admitted, is a risk factor for permanent mental impairment. It's also a disqualifier under the Nuclear Weapon Personnel Reliability Program, which raises questions over whether Obama should have authority to use such weapons. Glass houses...stones...
Having head about DailyKOs, Du, and Moveon.org, it doesn’t surprise me that you find that stuff on Obama’s sight. I wish folks who are reasoned would go over and look around, finding the things you have. What it proves more than anything to me, is that there is a wing-nut faction on the left that is just about certifiably mad.
Normal folks need to know that. Do you want to line up with these wing nuts? Obama aside, I sure wouldn’t.
You take care.