My understanding of the reason FTL travel is impossible even if (huge if because it requires infinite energy to start and stop) we could somehow figure out the boundaries, is that it breaks causality. Causality travels at the speed of information and to my understanding that is at c. If you launch a ship in response to a signal, and the ship goes faster than light, you have the potential for tge ship to arrive before the signal summoning it is sent. And this assumes that all the negative energy and negative mass and space debris problems are actually surmountable by beings anywhere in the universe. If you’re talking about breaking causality, either we admit that we know literally nothing about anything in physics, or we admit that we’re likely talking about a fantasy and we’d get equal results by spending billions to try and mix Floo powder and travel across Europe by fireplace.

As for wormhole theory, I’m not sure it actually fairs much better, unless we’re going to start dosing up pilots with worm-puke gas until they turn into fish-like superhumans who can predict the future.