The article clearly stated (if you'd have read it) that the company allowed such things in cubicles; expressions of political affiliation, what have you.
Ten bucks says the guy's supervisor is gay.
I've read the story as written at Agape's website as well as at Pacific Institute's site.
The problem is not what the article clearly states (which isn't much), but it is interesting to note what is missing.
The who is missing (both the company and the employee)
the what is missing (what did the bumper sticker say)
the why is missing (why did the employee get demoted - we have only one side's response to that)
The where is present (it's in California)
The when is assumed (as in it happened recently)
This article fails to provide sufficient information on which to base a conclusion one way or the other, and the information that is provided is definitely spun in favor of the "aggrieved" party.