I am not saying that philosophers should refrain from engaging in political activity; my target is instead the politicization of philosophy itself. I think that the conduct of the profession should be as bottomless as its subject matter: If we are going to have professional, intramural discussions about the ethics of the profession, we should do so philosophically and not by petitioning one another. We should allow ourselves the license to be philosophical all the way down.
“But I need to get people to see that excluding certain voices is not the way to create an inclusive intellectual environment.” Then argue for it! If you strip the list of signatures off your petition, you’ll find that you have an argument on your hands. The argument was there all along, but only when shorn of the appeal to authority does it invite counterargument — as opposed to counterpetitioning. Philosophers value having opponents worth listening to; we shouldn’t be trying to sort people into teams of the like-minded.
There are reasons why someone might sign a petition -- to get something on a ballot, to register an administrative complaint, and the like. You can tell a lot about a petition simply by asking what practical problem it addresses and how it is proposing to solve it -- indeed this is the only serious standard of evaluation for a petition, by its nature, since all petition is for the purpose of petitioning. (One of the most amusing kind of protests I have seen from the petitioning crowd is that people don't petition to persuade; but the notion of petitioning depends for its coherence on petitio, requesting or applying for a particular kind of behavior. There is no sense in which you are genuinely showing 'support' for anything by signing a petition unless you are signing it in order either to change things or to prevent some change.) But certainly it is true that most academic petitions are not of this sort, and their value thereby reduces entirely to whatever argument they offer with the signatures stripped out. I would actually go beyond Callard and argue that the argument represented in a petition is almost always extremely poor; the arguments that are put on petitions are often quite generic and based on widespread prejudices more than serious study, because they are formulated with the end of getting signatures rather than with the end of giving a rational account of things. You get better ideas and arguments by avoiding petitions.