You don't need a full-on monopoly. All you need is for a megacorp to have enough of a stake in a group of companies that it can dictate certain policies due to

You don't need a full-on monopoly. All you need is for a megacorp to have enough of a stake in a group of companies that it can dictate certain policies due to the damage it could cause by tanking the share price if they don't play ball. Something like "All of you must adhere to this ban list that we will keep updated". The megacorp doesn't outright own them so there's no monopoly, but that hardly matters to the poor sod who can no longer buy food because every single food-selling outlet in his area is affected, and toeing the line. And it wouldn't even need to be this nefarious. Like all paths to hell, it could start with a "bad people" list that becomes homogenized across the companies because one of them has special skill in this area and it's cheaper that way. Then the list starts to expand, and since all of this group of companies are linked, they all follow the same ban, use the same facial recognition etc.