I would be much more frustrated if they became cheaper and reduced the quality of the product.
Whenever I meet one of these people, I ask if they are willing to negotiate a wage reduction with his HR. My logic is simple. If you think it is wrong for a business to sell a product at the maximum price they can demonstrably get away with like Lego does, then why is it right for you, a professional worker selling your labor, to sell your labor at a price higher than what is necessary for subsistence?
That's actually how competition is supposed to work in capitalism. If you sell your products at much higher than the minimum price, someone else can make a profit by selling slightly cheaper and taking over your market share.
I think what the commenter is getting at is that it's not even about competition. People get mad when companies charge more than is necessary to make what they deem a reasonable profit.
Of course, as you mention, in capitalism, a competitor is free to go in and undercut the leading brand, but they have to be able to sell why they're better AND cheaper.
If Lego was nationalized then the excess earnings that go into the owners' pockets as dividends or asset value would be realized by the people. But that of course leads to different inefficiencies (investors don't invest, etc...).