Another conspiracy was that a CIA agent was very displeased with Kennedy becoming president. Many CIA agents lost their jobs after the failed invasion of Cuba called The Bay of Pigs. Many believe that these agents became so upset that they decided to scatter around the plaza in Dallas and take Kennedy's life.
Although it's very obvious that historical criticism sticks out, Marxist could also be seen very slightly. Many people who don't believe the theories because it "can't happen to a president." Or maybe they think "there's no way someone is this smart." They don't ever consider the "What if?" part.
Thomas, Evan. "Who Shot JFK?." Newsweek. Sept. 6 1993: 14-17. SIRS Issues Researcher. Web. 05 May 2015.