Why do you have to show a receipt and allow store employees to search?
Because that is the process of the store you're choosing to buy from. You have no obligation to buy from that store. If you dislike their policy, you should let them know and choose not to shop there. It appears, from your comments on other answers, that you're talking about Walmart. The main reason they do this is that they work on extremely thin margins. They make their money on volume, not necessarily a big markup on items. So shrinkage/theft can be a big problem. To ensure that customers are not taking more with them than they purchased, they check receipts (in some locations - I've actually never been stopped at a Walmart for a receipt check). If you find this offensive, let them know - verbally and with your dollars. Shop elsewhere. Or accept that the price of cheap stuff is a little extra inconvenience.