The question’s a little weird.

Can a reasonable person genuinely believe in ghosts? Yes, obviously, people do and many of them would be considered generally reasonable. They manage their lives okay, they make good decisions most of the time, they’re not gibbering maniacs, they’re reasonable people.

But: is it reasonable (meaning, grounded in good evidence) to believe in ghosts? I’d say it depends on what you and your friend specifically mean by “ghosts”, but in general no. If ghosts were real, they’d be more observable.

And “Hitchens said so” is pretty weak sauce, so I hope that’s an uncharitable summary of your argument.