The government controls a LOT of what we can buy already. Sex work is highly regulated, and you can't buy people. You also can't buy endangered animals, ivory, or nuclear weapons.
In terms of people spending money on what they want, people spend lots of money on opioids and it ruins their lives, or kills them. Should doctors and pharmaceutical companies not be bound by any regulatory body? Should people just be allowed to OD on fentanil because they want to spend their money on it?