I agree with you, OP, inasmuch as it's rather stupid and short-sighted to just assume that you can go on shoplifting forever and ever.
If lots of people are shoplifting, and then they're fencing the goods to lots of other dishonest people, who then spend far less in the shops, there has to come a tipping point when it's simply not sustainable for the shops to stay open.
What will the thieves - and sadly also the rest of us - do when previously easily-available goods are no longer obtainable, just because too many people believed that the idea of actually paying for stuff they want was beneath them?
Even the mighty supermarkets only get rich on very high volume of sales, rather than huge profit margins per item. I'm sure I read that they make in the region of 3-5% overall profit on every item they sell - so if one thief steals one item, that means there have to be 30 or more honest shoppers to come along and buy that same item for the shop just to break even on it.
As PP said, shops could go down the Argos route and keep all of their stock behind a counter, only handing it over once it's been paid for. However, that naturally increases risk significantly for the employees, as the determined thieves will see them as just another obstacle to overpower and/or threaten to get the goods, now they can't just help themselves whilst the employees can at least look on from a safe distance. Maybe they'll do away with human assistants and just use tough lockers instead, which can't be opened and the goods taken until payment has been made.
In reality, before long, I think most shops will be following the new high-tech model whereby you're automatically identified as you walk in - and your payment details validated before you're physically able to gain entry - and then every item that leaves with you will also be automatically identified and charged to your account.
Even this will be easy to defraud, though - but it will be ordinary members of the public who are stolen from and put in great danger rather than the shops and their employees. I'm certain it will become commonplace for thieves to slip expensive items into other people's shopping - probably deliberately choosing elderly or otherwise vulnerable shoppers - and then following them and demanding it from them as soon as they step outside the store, having unwittingly paid for it for them.