Some years ago I looked at Facebook's ToS for implementing "log in with Facebook" and at that time it looked like it precluded an implementation that would only send requests to Facebook if the user chose Facebook login. I don't think it's for sure that disqus could fix this problem if they wanted to.
Back in the day, Heise apparently caught some flack for protecting their readers while still allowing Facebook "likes".
It feels to me like the typical Facebook approach: do what they want to do or a little bit more, monitor the blowback and walk it back as little as possible only if required to keep everyone happy.
That was basically just a trademark dispute. They claimed it was confusing to show a Facebook "like" button that didn't work like Facebook's actual "like" button. It's fine if you use your own assets to indicate what the button does, but you can't use a Facebook logo or their thumb icon.
I understand Facebook chose to use trademark law to threaten to block the Heise app id and even their entire domain (any sharing of the paper's content on Facebook).
Facebook continues to use every tool at their disposal to protect their expansion of the privacy invasion of their product.
The facebook SDK surely can't reliably tell if it was loaded on page load or only after the user clicked a "Facebook" button? And they support OAuth, so you don't have to use their code at all on the client side.
I don't know the details, but I can't see a reason why they can't just not include the SDK until they need it (sure, this will add a delay before they can use it, but seems better than this current implementation for privacy!).
It's obviously in facebook's interest to load the SDK as much as possible. Even if you are not logged in, they can get a lot of valuable tracking information from the server logs, including IP address, referrer, any fb cookies other than login, etc. In fact, so long as a client loads the sdk on multiple sites, even if logged out, Facebook can still track that client across sites visited (simple list of referrers associated withvthis cookieset)
