Do not confuse "no indication that [nuclear energy] will ever be obtainable" (there is no evidence that it is an achievable engineering feat) with "it is impossible" (it is explicitly not permitted by physics as we understand it)
There are FTL proposals that do not violate known physics, such as distorting spacetime using some perhaps yet unknown mechanism.
Saying that there are hard limits in physics here, as you did, suggests that research in this direction is not worth our time.
I believe that is misleading.