Jack Kerouac chose the themes he wrote about carefully and they certainly do reflect the time in which he wrote.
The theme of rebellion was important to Kerouac because he would have been rebelling against narrow-mindedness and tradition. As a result of the Cold War and more specifically the HUAC (House of Un-American Activities Committee), Kerouac would have rebelling against this committee which used terror and fear to intimidate people into believing what they wanted you to believe. Blacklists were created most famously in Hollywood and all filmmakers, actors, writers and others. who had ever had leanings towards socialist ideas or the communist party were rooted out and named. HUAC also encouraged people to name others involved in order to protect themselves. In On the Road, the main characters rebel against the government by ignoring it, mostly. And certainly this is Kerouac’s comment on the time in which he was living.
There are some great websites dedicated to HUAC and the infamous blacklists. Checking one of these sites out might make the themes in relationship to the time period even clearer.