The notions of private property and free markets are about moral vision and fairness. They are enforced with the threat of violence, and they benefit members of society unequally. Some people like to pretend that they’re natural, that they’re a given, and that challenging any component of them is imposing one’s own morality on some God-given system.
That is false. No economic system is more or less about morality and fairness than any other. You believe in letting the capital retain more of the earnings than the labor because you think that is moral. It has nothing to do with some supposed position of neutrality.
And if we consider all of the locally owned retailers that have gone out of business due to Walmart's (admittedly efficient) business practices, then saying something like "Walmart doesn't need to exist" really isn't that all that crazy.
Now, you're upset about the residual $z-$y coming out of your pocket. But you might instead be grateful that Walmart is kicking in $y-$x to support your extravagant political demands. That's the subsidy.
> it's much better for me to be making up the hidden costs of chronically underpaid workers
Those workers are only underpaid according to your notions of fairness. You think _Walmart_ should be tasked with implementing _your_ moral vision at _their_ expense. I think _you_ should be tasked with implementing _your_ moral vision at _your_ expense.