We don't have experience dealing with the psychological consequences of certain death among thousands of people confined in a tin can without any chance of exte

We don't have experience dealing with the psychological consequences of certain death among thousands of people confined in a tin can without any chance of external help. To prove your theory, we would have to gather these thousands of people in a dome in the middle of nowhere, not help, not let them leave at all costs, and maybe enforce a % of deaths to simulate what could reasonably happen in space. Find volunteers for that.