"The important point is to keep the fracture under control. Hack writers will assume that if we have to break a few theories of physics for FTL, why not just throw all the theories out the window?
Don't give in. Omitting physics will degrade your setting to a pathetic lack of believability worse than an average Space Ghost cartoon.
Ultimately, the goal in writing good fiction isn't "accuracy", it's believability. The goal is to take the more fantastical elements and give them a sense of verisimilitude. For science fiction, scientific accuracy in anything not hand waved for the good of the story is a good start. If you want to preserve the sense of being real, you have to diverge as little as possible in your hand waving."