From his new book, "Cinema Speculation" (boldface added):
[T]he Pod People transformation is closer to a rebirth than a murder. You’re reborn as straight intellect, with a complete possession of your past and your abilities, but unburdened by messy human emotions. You also possess a complete fidelity to your fellow beings and a total commitment to the survival of your species. Are they inhuman? Of course, they’re vegetables. But the movies try to present their lack of humanity (they don’t have a sense of humor, they’re unmoved when a dog is hit by a car) as evidence of some deep-seated sinisterness. That’s a rather species-centric point of view. As human beings it may be our emotions that make us human, but it’s a stretch to say it’s what makes us great. Along with those positive emotions—love, joy, happiness, amusement—come negative emotions—hate, selfishness, racism, depression, violence, and rage....
Imagine in the fifties, when the [first "Body Snatchers"] film was made, that instead of some little town in Northern California (Santa Mira) that the aliens took root in, it was a horribly racist, segregated Ku Klux Klan stronghold in the heart of Mississippi.
Within weeks the color lines would disappear. Blacks and whites would be working together (in genuine brotherhood) towards a common goal. And humanity would be represented by one of the racist Kluxers whose investigative gaze notices formerly like-minded white folks seemingly enter into a conspiracy with some members of the county’s black community. Now picture his hysterical reaction to it (“Those people are coming after me! They’re not human! You’re next! You’re next!”).