Well, I know an essential characteristic anyway. You want to know what best describes reasonable people? I know.
Reasonable people are the ones who accept the results of science.
Conversely, unreasonable people are the ones who reject the results of science. Since religious believers (theistic or otherwise), believe in at least one doctrine that goes against the consensus of scientists working in their fields, then religious believers are not reasonable people to believe them.
Agnostics are also not reasonable people by the same standard. For by claiming not to know about a specific doctrine that has been shown to be false by science, they are not reasonable either. Saying they don’t know, when science knows, is to be a science denier.
Debunking Christianity