The argument is that it's privacy neutral since this kind of tracking can already happen with JS or no JS with redirects both of which are widely deployed already.

* There's now a spec/standard for the data exchange.

* Users get faster websites, can see the actual destination URL on hover, and maybe a slight security improvement in the event that the server component performing the tracking redirects is compromised.

* It's easier to find the ping attributes on links than untangle all the JS on a page.

* For extension developers this actually increases privacy (assuming it's adopted en mass) because now you can just remove all the ping attributes on links rather than unbind click handlers which might end up breaking the page.