The Problem With PZ's Analogy

I'm finally catching up on Pharyngula, unpacking the bedroom be damned. I notice that he spanked Rep. John Shimkus for his "We can't cut CO2 emissions - we'll starve the plants!" and "God won't let global warming destroy the earth!" idiocy. In doing so, he makes a comparison:

However, please note: human beings aren't plants (well, most of us, anyway — John Shimkus does seem to share some similarities with root vegetables).

It would be a great analogy, except for one thing: root vegetables are useful.