They might as well call him poopyhead, because the goal here isn't to identify Obama as a Marxist, it's to collectively scapegoat him, just like how children will gang up on another child. They don't know why they're yelling names other than it makes them feel part of something that validates their innate meanness.
edit: A bit of satire on the subject http://www.huffingtonpost.com/2009/09/22/protect-insurance-compani_n_294406.html