There is nothing to counter this argument. The Return-Portkeys we used to get back to headquarters both after the Manor reconnaissance and the Sheffield mission were only distributed in the equipment room shortly before each departure. It's an additional security measure that the Portkeys aren't readily available to everyone. A measure that makes perfect sense and actually keeps me from leaving this roof. Camp Black is the safest place for me and I would never take the risk of not being able to come back. Blaise knows that, Potter knows that. And accordingly, I can now hang around up here, let the wind blow in my face and grapple with my dark thoughts.