"I still believe in e=mc², but I can't believe that in all of human history, we'll never ever be able to go beyond the speed of light to reach where we want to go," said Clark. "I happen to believe that mankind can do it.
...
Gary Melnick, a senior astrophysicist at the Harvard-Smithsonian Center for Astrophysics, said Clark's faith in the possibility of faster-than-light, or FTL, travel was "probably based more on his imagination than on physics."

Gary Melnick is the nerd, not Clark- Clark is a wannabe.
Nerds, of course, have that failing of focusing on details which aren't particularly significant. The FTL limitation has little to do with the feasibilty star travel. If we could generate speeds of say 1/2 the speed of light (and therefore not be anywhere close to violating Einstein physics) humans could travel to the stars- if not for other more significant limiting factors- such as the laws of economics.
Just as the reasons we can't get off Earth, the problem of star travel will be mostly about political and economic barriers- if there is a big enough benefit to human beings to travel to the stars, in comparison to it's costs [either humans are very, very rich, or said differently, costs are dramatically lowered] then human will become capable of stellar travel.