If users want to scroll endlessly, they should be able to, and they're going to, regardless of what scrolling implementation a platform uses - I scroll through many pages of HN just fine without infinite scroll.
Kinda sad more and more Web sites switch to pointless AJAX app model recently and it stops working for those.
But oftentimes it's the only option available, and it's garbage for everything except mindless scrolling.
* sin count taken from the Iron Maiden song.
Infinite scroll gets higher “engagement,” then pagination. Those are people who kept scrolling, who wouldn’t have otherwise.