Only 550 people have been to outer space and most of them were highly disciplined military officers. However, one of them named Lisa Nowak lost their shit shortly after a space mission on the STS and attempted to kidnap and probably intended to kill a romantic rival. They cannot psychologically screen people well enough to send them off world for a very long period of time. All it would take to destroy the multi-billion dollar space station, planet colony, or deep space ship and kill everyone inside would be a really pissed off person with a screwdriver, because beyond the skin of the ship or structure is instant death. When the station went dead we'd never even know what had happened.

Resolving a romantic disagreement in deep space could only be done by kicking one of the quarrelling couple out of the air lock, since they can't exactly put a restraining order on anyone there. What if someone decides they have had enough of a crew mate after four years and smashed their skull while they slept? What would happen if they admitted it, and by the way they had fabricated a scary looking weapon? I guess they would be the new commander.

Only the clueless who think that flawless people can be found or created would think that space colonization is possible. Years of isolation IN A POD will be too much for most people to take.