> They can't do anything about cartel behavior.
Incorrect, several states have passed their own antitrust laws, there's nothing that limits it to the federal government.
> The government engages in commerce all the time. If we took that argument to its logical conclusion there would be no libraries as they compete with book stores. There would be no armies as they compete with Blackrock mercenaries. No public transit as it competes with private transit. No public events as that competes with ticketmaster. No public schools. No public universities. No scientific research grants. No sheltering or feeding the poor. No treating the sick. No treating veterans. No bridges. No roads. No harbors....
I do think the government should get out of many of those, so your argument doesn't really land for me.
> No, it seems a big role in this country for government is facilitating conditions for commerce.
I don't see how the government driving out competition by running its own grocery stores, presumably at a loss, is "facilitating conditions for commerce".