I think what the grandparent meant was that if you were not using the land profitably you are going to want to 'sell' the land to someone who can use it more profitably and is therefore willing to pay a high price for it. If you didn't do that and just rented the land you would lose money because of the high land tax.
I think 'selling' here means "giving the other guy the privilege of having to pay lots of taxes instead of you".
I think renting land in any fashion is morally reprehensible. Though I don't fit in with much the neoliberal HN crowd as an anarchist communalist.
Ownership should be restricted to the community of inhabitants of the land. The processes around controlling the land would be voted on democratically, and a federation of community ownerships with local representation would deal with extra-community processes around broader land decision making.
I think 'selling' here means "giving the other guy the privilege of having to pay lots of taxes instead of you".