The only use I know for captive portals is EULAs, and I'm not sure those ever had legal weight (though obviously IANAL).
But honestly they were starting to be outdated (technologically) even before this. Since a lot of popular sites use HTTPS, I usually have to try and think of a non-HTTP site before I can get through. They're just a nuisance at this point.
This is not to defend Google's actions as "altruistic" in any way. But sometimes Google's interests and the public's do align.