This is something of a famous quotation but Google isn't helping me. He basically says "let them become martyrs" and is disgusted by their willingness to sacrifice their lives for this ideology.
Not sure if this is what you're looking for, but Marcus Aurelius in his Meditations criticizes the Christians for their eagerness to blindly face death rather than actually reflecting upon what it means.
The full quote (from Book XI) is:
"What a soul that is which is ready, if at any moment it must be separated from the body, and ready either to be extinguished or dispersed or continue to exist; but so that this readiness comes from a man's own judgement, not from mere obstinacy, as with the Christians, but considerately and with dignity and in a way to persuade another, without tragic show."