Sure you can argue that way. But it's not as big of a problem as you think it is. The fact that Apple does it is enough proof for that.

Websites can be changed to work without third party cookies. I'm blocking cookies since years and I have come across less than 10 sites that require it. When that happens, most of the time I just go elsewhere or I'll send them an email.

I’ve been blocking third party cookies for as long as Safari has had that option, and I’ve never noticed an issue. I only get Google’s annoying recaptchas when my search string is too specific for their tastes.

What sites are broken by Safari because of its default cookie options? I haven't encountered any.

Any site which iframes in another site where you're expected to be logged in. For example, Disqus comments, Facebook like buttons, Youtube embeds (which work, but show ads even if you've paid for no ads).

There are also lots of one-off cases where developers split functionality across multiple domains in ways that were fine at the time but now get blocked. These are all fixable, unlike the iframing case, but it's still a lot of sites.

We need to redefine 'break' into:

Breaks because it was abusing lack of FPI.

Breaks innocently.

I think it's more nuanced than just blocking ALL third-party cookies. If you have visited the site before (e.g. facebook.com), my understanding is that those cookies are allowed. It's only blocking third-party cookies from sites you have never explicitly visited before.

Atlassian's HipChat web app breaks (in Gnome Web, which also disables third-party cookies).

<snark>So, nothing you'd want to use.</snark>

A large percentage of things that break SHOULD BREAK. That's the whole point isn't it?