Except that loose carts roll away and get blown by the wind scratching other people's cars. Carts put up on curbs and in gravel etc. ruins the wheels making everyone's experience worse. Carts left in the parking lot block spaces so people can't park in lots that already sometimes are overfilled.

You're not 'sticking it to the man,' the store owner or corporate shareholders who make the rules and set the prices don't care, you're making life worse for your fellow shoppers.