Just start an opposing petition: they're trying to make fatties a protected class?  Write one up supporting preservation of the currently defined protected classes and specifically calling out the choice to become obese as an example of what should not be included in that definition.  May have to speak the language of the SJW to make it palatable for some but it can be done. I agree though -- I'd like to be able to sign against a petition.  Kind of a garbage system.