On the other side, I could just say the exact opposite: I find it infinitely easier when a site supports Facebook authentication. You can't just say "it can also work against you" unless you can show evidence that the target audience of the site, on the balance, will be turned away.
I mean, if we come up with more of these, eventually everyone will find at least one ludicrous. "I for one will NOT use any web site that requires"... "a credit card", "watching advertisements", "authentication of any form", or (probably the only reasonable one ;P) "seeing comic sans".
Actually he only needs one example to say "it can also work against you", and he is that example.
He didn't say "will", or "probably will" even, just "can".
But using FB to login to other sites seems less handy and more like a way to lose all your accounts when one of them gets hacked, and by concentrating so much value in a single account you increase the likelihood of it being targeted.
That is like saying chemotherapy "can work against you" by showing a single skin cell died during the treatment; it isn't "working against you" unless you lose so many skin cells that the chance of killing the cancerous tumor is no longer "worth" the risk.
If you accept "single user got angry" then every single thing you can "can work against you", and the phrase is meaningless: some people hate the color blue, while some other people hate everything /but/ the color blue. Decisions need to be made "on the balance", not because there's one angry user.
I mean, if we come up with more of these, eventually everyone will find at least one ludicrous. "I for one will NOT use any web site that requires"... "a credit card", "watching advertisements", "authentication of any form", or (probably the only reasonable one ;P) "seeing comic sans".