While prison likely has a high concentration of pathological personalities, the more serious the company you are in, the more it will have collected people who are attracted by power and prestige - the more probable case that you will be dealing with psychopaths.
The ones I've met aren't actually that smart (handwavy estimate is they seem to top out around IQ120), and usually only have one or two blunt but heavy social tools that make them high functioning manipulators. They are enabled by overly trusting, high IQ but socially unsophisticated engineers who are easily bullied.
With violence largely a non-factor in a psycho's toolkit in the startup world (vs. prison), you can learn to anticipate and manage them.
While it can be fun to have the scariest dog in the park, who's just a sweetie to you at home (because all they understand is power), it raises the question of responsibility. You know it's going to do harm, it's just a matter of time, and the question for a real leader is, at what point do you recognize it for what it is and put it down?
If you have ever been to boarding school, summer camp, or worked in a large institution, the difference to prison seems largely symbolic. Different people and rules, yet still, people and rules.