I'll leave it as an exercise to the lurkers to decide who is probably right.
Yes, that is how these things tend to work! Seriously, read some books on antitrust, you have no idea what you are talking about. Tim Wu is a good starting point.
The effect of antitrust would then be that Google separates the ad service for its own services and third party services, which would force their third party ad service to become more expensive since it can no longer rely so heavily on the draw of all the Google properties.
I suspect this is what what @arrosenberg is getting at. If the Search (and maps) business is considered separate from the ads business (Search runs at a massive loss) and it's provided for free because they can subsidize it with the revenue from their ad business, then it's an anti-competetive advantage they have from a monopolistic position that their advertising business has.
Anyway, personally I have no clue how that "works" in practice, but that seems to be the perspective.
A single company, google, gives a photo-service for free, while making enormous bread through ads. On its own the free service would be dead on arrival but now it's sustained by the ads branch of the company, making it unbeatable. Then pure-photo-service competitors die and you get a monopoly.
