The problem with traveling at the speed of light is getting there. It requires an infinite amount of energy, which is just impossible for us to achieve as human beings (since our rest-mass is not zero). The best way to describe it is that all of the mass in a photon is due to its energy, and so it moves at the speed of light. But if all of our mass were in energy form, that means either we would be made of mass less particles (like light) or we would have essentially zero rest mass compared to our energy (which means our energy would have to approach infinity). And since mass generates gravity, your infinite gravitational field would be generated by you, and you would become the center of a new black hole if you ever put that much energy in once place. Also, there isn't an infinite amount of energy in the observable universe, and as we know we simply can't compact all that stuff into one place feasibly.