Thanks for sharing your perspective. Just to make sure we're on the same page, you are arguing that FB engineering was 100% aware of the consequences of automatically switching primary email address to @facebook.com for users who had setup that functionality, including overwriting email addresses in phone contact lists and capturing email unintentionally sent via those modified contact lists?

This is certainly within the realm of possibility and indicates that you hold the team's technical ability in high regard. If it is indeed true, I would wonder what percentage of the folks involved in the implementation actually thought about it and how high/wide the issue was escalated. I have certainly been in situations where after-the-fact I found out that something I had been a part of shipped with known bugs/features I didn't know about that I would have raised a lot more concern over.

My line of thought is that they knew it would change phonebooks and that they weren't putting whatever resources necessary into creating a process for rollback. Given the nature of Facebook and it's technology, I'm not even sure there is anything they could have done, but it's de rigeur to know if this is the case. It's not even about high regard, but by minimum standards. If you know you can't rollback you go full steam ahead.

If you've never worked someplace where they have dedicated staff for source control, that fact alone might give you an idea at the level of expertise involved here. It's nobody's first time at the rodeo, and setting the sync API on the change (as described below) wasn't just slipped in by an intern.

You finding out after-the-fact and still having an opinion about bugs shipping in code you contributed to only reinforces my point: someone made the decision to go ahead anyway.