IMO buying defaults isn't as bad as Google's rigging the ad market. At least others have outbid them for search defaults in the past and in other markets.
That one is definitely a lot worse and a danger of a monopoly/extremely powerful market player. I would argue that a monopoly is not inherently "bad"* but has much more ability to do bad things if it chooses to, with not much potential recourse from others.
*Strictly in an ethics and fairness sense. It might (or might not) be worse for consumers. Just worse in a kind of boring rather than nefarious or deeply harmful way.
