Ok, I still don't think it makes much sense. The line in a race is set up for fairness to the runners and spectators, not to advantage the authorities. So stepping up to the line doesn't serve the authorities unduly, which is the claim made against Tim Cook. Also, the runner does not have a more honorable alternative. Running in the bleachers doesn't serve him better in some way than running on the track from the starting line. Pulling a weight for someone else as in the image of 'towing the line' still fits better in this case.