Oh, how dastardly! But no, not really. At the second Diet of Speyer certain attendees drafted, signed and presented the Protestati, and those who subscribed to the document naturally became known as "Protestantem," which is the present participle of "Protestati."
It could have been worse. Imagine what you people would be called if they'd given the document a silly title, like "The Complaint," or "The Testament to Hurt Feelings." Count your lucky stars.
Well we could say we complain about how Christ is treated, or about how the heart of God was hurt, and what’s it to ya?