I guess we can debate whether he truly understood and embraced Marxism or whether it was simply something he found that answered his questions as to why the world he grew up in was so miserable and so unjust. Which, in his defense, it largely was. Perhaps a bit of both (and I do think some of the key concepts of Marxism were understood by him in some detail; if you correct his spelling and grammatical errors in his writings, as Noman Mailer did in his book on Oswald, you can see that they're somewhat sophisticated).
But the evidence that he disliked, indeed hated, the American political and economic systems is, for me, conclusive. He found it unjust and irredeemable. Indeed, he told Michael Paine shortly before the assassination that the American system had to be completely overthrown, that incremental changes would not work. It could not reformed; it had to be replaced. And in a Marxist/leftist type direction.
The only response to all of this is, as Weisberg and Garrison argued, that it was an act or a cover; that because his favorite TV show as a teenager was about a man pretending to be a Marxist (Herbert Philbrick) that he too was acting out this fake life. Either for his own bizarre reasons or because he was directed to do so by others. I find it quite unlikely that someone would direct him at the age of 16 to create this cover or "legend." For what purpose? But then again I'm not a JFK conspiracist.
Oswald was an angry malcontent dissatisfied with his place in life. He blamed everyone except himself. In American society, he could turn to Marxism as a means to be the anti-hero. Oswald needed a platform to vent his personal anger and Marxism provided that. In addition, being a Marxist gave him notoriety as an outlier that he apparently desired. He would not have been sought after for interviews if he had adopted a mainstream political cause. I think his political beliefs were superficial in comparison to his own psychological impulses but that they provided an important mechanism for his violent actions. It allowed him to view himself not as an angry nut but as some type of political revolutionary hero.
