Most technical people I've met who bemoan the "fact" that they would make more at their company as a manager (mediocre or otherwise) would also have the option of moving companies and/or industries to a technical role that pays better. And yet, they don't. Mostly because it turns out the preference isn't just about $$, but about all the other factors (I don't want to move, I don't want to work on X, I only want to work on Y, it's too big, it's too small, they don't give enough holiday, whatever).

So what it really comes down to is that they disagree with the company about how it values their relative contributions. Which is obviously fine, but do you really think the average IC has the data or experience to evaluate this well? Many of the rants I've heard along these lines were pretty naive about the business.