Private transactions occur within the wider public sphere. There has never been a private transaction (of any considerable value) that does not have significant consequences for society.
Insisting that reducing transactions into private and solely monetized coercive (the legal machine plays its undemocratic role here) agreements means that all other human and social values are banned. Freedom is replaced by money transactions while proponents claim money is freedom.
When this ugly distortion attains social dominance, as it has, then accumulations of capital and its debased ideology dominate beyond democratic control. Oligarchs rule, democracy withers, money replaces human values, and corruption becomes rampant in society. Money becomes an end in itself, subject only to the money Gods.
Then, on Sundays, they ‘worship’ god, some even claiming that this is what their Sunday god teaches!