We trusted Facebook with our data.

We trusted Facebook with our data. Facebook decided that trusting third parties was easier than properly restricting access.

The quiz app violated Facebook’s trust by violating terms of service.

Facebook violated our trust by making that possible.

Like you said, the single sign on functionality is very useful. Facebook doesn’t have a monopoly on that functionality though.

Here’s a security talk from 2010 highlighting some of their issues, but putting too much (IMO) of the blame on users instead of Facebook.

Why should we continue to trust a company that has repeatedly violated that trust? There are other options and if they suck too, we can make more.

Facebook should fail for their actions. Capitalism at its best.