> It all seems very arbitrary Far from it. We know that markets perform best when there is lots of choice. Monopolies are bad for various reasons, but one of t

> It all seems very arbitrary Far from it. We know that markets perform best when there is lots of choice. Monopolies are bad for various reasons, but one of them is that it can be leveraged to gain a monopoly in other markets, as described by a sibling comment. This is market economy 101, you could read up on the context of anticompetitive legislation.