This movie is not so much about aliens who are hiding among us, but instead it taps into the deeply submerged suspicion held by most of us that we are being manipulated and taken advantage of by the elite of American society, by our leaders, by the rich, etc. Also, we sometimes feel that we are manipulated and programmed (in a subtle way) to respect hierarchical authority ( e.g., the "OBEY" subliminal command from the movie).
Some leftist thinkers might say that human societies are in a way being parasitized by the elite of their societies, and that the elite operate as a parasitic sub-society, living off of the lower classes. America might be said to be operated more in such a fashion (i.e., parasitized by the elite) than are the countries of western Europe. Obvious examples of this parasitic behavior are the "golden handshakes" and backscratching exchanged between corporate CEO's and the Boards of Directors of their companies. But it is far more pervasive than just that.
_They_Live_ uses the invisible alien elite as a proxy for our suspicions about how we are all being exploited by the elite of our real-life society, and how these elite are subtly programming us to accept this exploitation.
So, the major theme of the movie is not, as another poster correctly pointed out, about being manipulated to be good little consumers in a crassly commercial world. No, it is far more profound than that. Instead, it is more about how the working class Americans in _They Live_ are being exploited by the elite upper crust, who, in the movie, happen to be aliens, but who, in the real world, are a subsociety that use their collective power to exploit the rest of us.
Unfortunately, this movie sometimes has an unintentionally comic air to it. Still, the exploration of that theme is so rare in pop culture, and that theme is so profound, and reaches so far into what American society is, was, and is becoming, that this movie is a Must-See for anyone with an interest in politics and sociology.
