Critics of high executive pay on the soft-core / moderate left (as opposed to the hard-core socialist left) often argue that they are not against large incomes per se. However, they argue that high executive pay is often the result of a failure in the structure of corporate governance, where a group of cozy insiders on the board and management hand each other compensation packages to which the rank and file of shareholders would be opposed (a subset of the agency cost problem).
I am somewhat sympathetic to this argument, as I have personally observed instances where I thought boards and management were too cozy by far. However, no one has really succeeded at proving this hypothesis on executive pay, and in fact shareholders when they have had a chance to vote on such packages have never really made a meaningful dent in them, and one can find a number of private companies where such governance issues presumably don't exist but high executive compensation packages can exist.
Just as an aside, a classic example of this can be found in the fabulous book "Barbarians at the Gate" about the RJR Nabisco takeover fight. The book does a great job of portraying a company with horrible corporate governance issues that seemed to be used to enrich managers with both salaries and perks, but then observed that the new private owners of the company gave their new CEO a compensation package that might have made the previous executives blush.
Anyway, I am yet again off the point. My point was to observe that the mainstream left seems to believe that there are corporate governance issues at large corporations that disenfranchise the majority of shareholders vis a vis key decisions involving the company executives. So I have to ask myself, if this is a real fear, then how does one justify having the President of the United States effectively fire the GM CEO, without any vote or substantial input from shareholders?
Postscript: It is all well and good to be cognizant of agency costs. Everyone should understand when an employee (or contractor or whatever) has different incentives than they themselves possess. For example, on my recent backyard renovation, I always kept in mind that my architect wanted to create a showplace that would advance his business and possible get into a magazine. In general, this alligns our interests, but there were times he pressed for things I did not value and I had to be insistent we were not going to do those things.
However, many folks seem to want to run off to government to do something about agency costs whenever or wherever they are found. This is hugely dangerous, as Congress tends to have the highest agency costs one will ever be likely to find.