We're not talking about protecting a political activist. We're talking about illegal rentals.
But regardless, if an attorney general asked The Pirate Bay or Mega for all personally identifying user data, I imagine people would be singing a different tune. Or, similarly, if an attorney general asked Google for everyone who had searched for "piratebay" or "mega".
> The legal strike comes just days after AirBnB CEO Brian Chesky tried to appease state lawmakers by agreeing that its users should collect the normal hotel occupancy tax and promising to work with pols to root out bad hosts.
http://www.nydailynews.com/news/national/state-airbnb-articl...
The appropriate summary is: AG specifically wants information about people who actually owe hotel occupancy taxes. They aren't trolling for every AirBnB user.
The difference compared to your hypothetical examples is that merely visiting the sites doesn't necessarily constitute illegal behavior. Searching for "mega" in and of itself is not an illegal activity, just like how searching for "marijuana" is not illegal (especially now that certain states have legalized recreational use). The true analogy is asking the torrent trackers to release IP information for connections pertaining to a specific torrent.
Whatever negligible externalities are introduced by Airbnb, they are vastly outweighed by positive effects like making travel more affordable and busting up the hotel oligopoly.
I felt compelled to point how ridiculous this is. There are tons of lodging options. You can see for yourself with a casual search on any price comparison site.
I travel quite a bit for work, and I've stayed at 30+ hotels over the last 2 years. All of them, with the exception of a couple independents in NYC, were owned by Marriott or IHG.