We already know the laws of thermodynamics has exceptions. In very small systems, the entropy of a system fluctuates randomly - up
and down. A light ray traveling over extremely long distances will have its energy reduced through red shifting, and that energy doesn't "go" anywhere, it is destroyed. In both of these regimes, over extremely small scales and extremely large scales, there are exceptions carved out of the laws of thermodynamics.
We know for certain that our understanding of physics is incomplete. General relativity (as formulated) is certainly wrong, because it precludes the possibility of small things existing; and yet they do. Quantum mechanics (as formulated) is certainly wrong, because it precludes the possibility of curved spacetime, and yet we know spacetime is curved.
There is, of course, a minuscule possibility that the emdrive actually works. It almost certainly doesn't. Ballpark one in a thousand. But we can't exclude the possibility that it works, based on the principle that the the laws of thermodynamics, which already has two exceptions, cannot have a third exception.
There's big talk about humanity traveling to other stars, colonizing other star systems, colonizing the galaxy and so forth. For this to happen, we would have to be wrong about physics. There's simply not any way to do it by building on the foundation of what we understand about the universe. So investing in low probability speculative ideas like emdrive is still necessary, even though for any given idea, there are lots of nines that say it won't work.