> half of Americans claim creationism explains the existance of man
This is a fantastic explanation, it just doesn't originate from science.
> 50% of Americans think there was a wider conspiracy behind the assassination of JFK.
This is a perfectly logical thing to believe even in the absence of evidence. It's reasonable for any assassination of a prominent figure.
> 35% of Americans think that global warming is a hoax.
This topic is super-politicized. Uncritical acceptance would be unreasonable (and many do accept one side of this without questioning it). Most people aren't going to do any research into the topic. The 65% who believe global warming probably didn't do any research either.
I think it's not even very fair to call these 'odd beliefs'.