> You say "seized control" like he showed up with a bunch of armed goons and wrested it away from its rightful owner. Craigslist dominates online classifieds because they recognized it was a market worth serving years before the incumbents in classifieds did, and served it. It's not a crime to get there first.

I agree that "seize" is poor word choice, but the fact that he gained a monopoly position through legal competition does not negate the fact that it's a monopoly.

>I must have missed the part where Craigslist used their dominant position in classified advertising to unfairly benefit other products they offer.

They use it to advance an unusual philosophy. Yes, this is different from using it to get money, but the effect for those of us who do not share their philosophy are similar.

If Standard Oil used the money earned from its monopoly powers to buy teddy bears for orphans, that wouldn't have reduced arguments that it was a trust and needed to be broken up. (And given Rockefeller's philanthropy, this isn't too far from the truth.)

Edit (since I can't reply): network effects keep out other competitors. I don't know what "unfair practices" are defined as, I just know that monopolies insulated from competition are bad. Somewhat analogous was Standard Oil's policy of dropping their prices below cost locally long enough for small competitors to go out of business, and then raising them afterwards. New competitors were prevented from entering because Standard Oil had a reliable threat of doing it again. This didn't require Standard Oil to apply horizontal leverage (i.e. using dominance in the market for one product to influence another).