Just because a particular group has high salaries in some absolute sense doesn't mean they shouldn't unionize. For one thing, unionization is nearly guaranteed

Just because a particular group has high salaries in some absolute sense doesn't mean they shouldn't unionize. For one thing, unionization is nearly guaranteed to raise salaries. For another, it will get them better benefits and working conditions. Overall, it reduces inequality, which is one of the major structural problems in our society and economy today.