Well, at least you get to pick between stores, right? If the people at the LensCrafters are being dicks while selling you different glasses all made by Luxottica, you can show them what you think of that by taking your business across the mall to the Pearle Vision. Or maybe the Sears or Target optical departments. Except that they are also all owned by Luxottica. Just for the sake of argument let's say that you're not a squinty-eyed nerd, so you pass by the prescription shops and go right to the Sunglass Hut. You guessed it. Luxottica.
That has got to be really heavy.
This is of course why they can charge you $200 for a piece of plastic with two hinges -- because most of the "competition" isn't actually competing with them. They are them. It also means that if anyone came up with a mind control chip you could put into glasses, they could have the whole world enslaved within months.
Keep Earth free! Get your glasses from Costco!