Doesn't it all depends on the domain you are working in? If you are artist, mathematician or academic researcher then you have don't have pressure to deliver something awesome in limited time or you die. In general businesses are game of survival of the fittest. Your competitors are always on move and you wake up every day hoping it's not your last as running company. You can't be startup founder with limited resource and also tolerate mediocre work or an employee. You can't butter up deficiencies and lack of progress. If you do what your competition can also do then it's most likely game over in few cycles. So you must demand 2X to 10X performance advantage in everything. This requires a certain degree of insistence and lower bounds on tolerance which would necessarily give rise to "meanness". This kind of environment seem necessitates ruthless people dictated by laws of evolution.

However I think meanness are generally not intrinsic, i.e., person isn't mean because they are naturally mean. It comes out because of the pressure of this survival game. You make a bad hiring decision and you don't have option to not let go the person even if they moved across country for you and took on expensive mortgage and have 3 school going kids. If you came to know that a competitor is going to release a product 6 weeks before you do then you might not have an option other than everyone work their every waking hour, including Christmas. Your admin brought down site 3 times because of an error and being "nice" to him risks this happen 4th time. And so on... These are the stuff painters, mathematicians and scientists don't have to deal with every day.