I don't know if this kind of thought experiment is authorized here, but let's give it a try. Let's assume that we had managed to build a spaceship able to travel at the speed of light. Since relativity forbids to accelerate until reaching such speed, the spaceship would have to reach it instantaneously, like a photon. But this is not the issue. The issue is: how could we operate such a spaceship? And I am not talking about levers and joysticks, but about establishing a course and reaching a destination safely. Because it seems to me that if such a spaceship was pointed towards, say, Mars, it would be impossible to reach this planet without crashing on its surface like a bug hitting a windshield. In other words, there would be no way to control the distance travelled. The conclusion being that the ability to travel at light speed would be useless.