All these various conspiracy theories invariably get started when someone produces some strong piece of circumstantial evidence with little bits of filler, people nod their heads cause it makes sense and because they distrust the person(s) it's being said about so it's easy to believe they might be 'up to something sinister'. This one starts off with basically three 'facts', his dad and step-dad were both muslim, confusing over the use of the word madrass, and the birth certificate thingy. They're not crazy, but after a while facts get muddled and people aren't used to actually taking something disproven and removing it from their equation, how many people think birds explode from eating rice or that its not safe to swim after you've just eaten? Both of those are believed by tons of people, most people probably, and have less 'proof' then Muslim Obama, Fake Moon Landing, Roswell, Sasquatch, and the guy on the grassy knoll.

None of this is really all that weird when you realize most people believe things simply because experts tell them so, which is entirely understandable, and that 'expert' to most people, is someone who knows more about something then them. If you ask people who believe in evolution to explain the theory to you, a large chunk will give you back confused gibberish, pretty much everyone believes in special and general relativity and thermodynamics, but I'd be damn surprised if one out of ten college graduates could give a coherent explanation of those. Very similiar situation to the JFK assassination, the government and media can produce mountains of evidence but to those who believe, it doesn't matter because they don't trust those sources.