Why is there no real speed Limit to Designing a Drone?

Because you don't have to design for a human being to survive in one.

Anything that the metal or electronics or plastics or other substances can survive, the drone can also survive at that speed.

Therefore there is no theoretical design limit to a speed at which a drone can be flown.

So, thinking about this the drone could be on fire coming from space into the atmosphere and as long as the control surfaces still worked it could still navigate by itself or with help.

Because of this it doesn't bode well for the ongoing long term survival of the human race here on earth.

They becomes a similar problem that nuclear ICBMS became during the 1950s and after in the U.S. and Russia and various other countries around the globe.