First of all, I would argue that it is somewhat dangerous to call something “propaganda” as that is a very loaded word. It tends to imply that something is promoting a point of view that is not true and is doing so in underhanded ways. Thus, it is something of a pejorative term that has no definite meaning.
That said, the message of this cartoon is simple. It is saying that capitalism brings us freedom and prosperity. It is saying that “Ism,” by which it clearly means some sort of communism or socialism, is a totalitarian system that will rob us of those things.
This cartoon was produced in 1948 as a way of trying to dramatize the ways in which capitalism and democracy were superior to communism. This was the very start of the Cold War era and many Americans were afraid that communism might become popular in the United States. The message of this cartoon is that people should not fall for the promises of communism. It is saying that communism promises prosperity but does not actually deliver. Instead, it oppresses people and steals their rights without producing any real benefits.
What the cartoon does not do is to specify exactly what proposed policies in the United States at the time were likely to move the US towards communism. Instead, it simply sends the message that communism is bad and capitalism and democracy are good.