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I think the difference is that your historical examples of skepticism (which are a bit exaggerated, btw. Da Vinci was a pretty bright guy who thought human flight was possible; Churchill summed up the current understanding of nuclear physics 99 years ago as "Might not a bomb no bigger than an orange be found to possess a secret power... to concentrate the force of a thousand tons of cordite and blast a township at a stroke?"; Konstantin Tsiolkovsky described the science of space travel by rocket in The Exploration of Cosmic Space by Means of Reaction Devices back in 1898)... your examples of skepticism are based on ignorance, not science. As far as I'm aware, nobody ever had a scientific rationale to think humans couldn't achieve flight. If so, it was obviously extremely flawed. We have well-supported science to support the idea that interstellar travel at human timescales isn't possible.

But any scientist will also tell you that there are potential methods to achieve interstellar travel that are consistent with our laws of physics. It's just that, unlike your examples, it's not a matter of human ingenuity to find them. It's a matter of the very nature of our universe whether things like wormholes or negative energy exist or not.