Monica at Mozilla: Tracking Protection for Firefox at Web 2.0 Security and Privacy 2015

Advertising does not make content free. It merely externalizes the costs in a way that incentivizes malicious or incompetent players to build things like Superfish, infect 1 in 20 machines with ad injection malware, and create sites that require unsafe plugins and take twice as many resources to load, quite expensive in terms of bandwidth, power, and stability.

From Monica at Mozilla: Tracking Protection for Firefox at Web 2.0 Security and Privacy 2015