Walmart screws the farmer with its Monopsony-power and uses that to undercut the small operater with its Monopoly power.
However much I might be inclined to agree with you, WalMart clearly just exploits the differences between two of the largest and least competent governments on Earth, via the loophole of global free trade. The Western farmer is 'screwed' because WalMart has opened a market of a billion consumers, while the Western retailer is screwed because WalMart can exploit those billion consumers as manufacturers. But they can only do this because both governments have abrogated basic responsibilities and instead of preventing abuse and trade imbalance, sanction it.
I agree with you, government must not abrogate its responsibilities as the Libertarians demand, and people should not abrogate their responsability to hold government accountable.
I think the governments job is indeed to provide public goods like transport infrastructure and law-enforcement, to uphold the social standards that decent people believe are above the market, healthcare and education? Hell yes. We demand the government we pay for makes itself useful to us and that these expenditures are not exploited by the selfish interests of would be
Robber-Barons while we the people abandon ourselves to the delusions and fantasies of the Austrian School.
There is a higher principal than power and money.
Capitalism is an animal, a useful animal to be sure, and the human must be its rider, not its grateful slave. We do not allow these corporate creatures of private power to consume everything in site and shit everywhere, we put the leash on the animal of capitalism and we say you cannot go there, you cannot eat that. You stay in your enclosure and apply yourself within the bounds of marginal social benefit and if you threaten the interests of the community of people we whip your ass and keep you in your place and say "Stay in your hole, dog, our highways and legal systems are not for you to fuck us with".
Yes, make money, innovate, but our children and the children of developing nations and our economic freedoms and the ecosystems of our planet are not yours to consume.
