Because security really is never a good reason to be skeptical and skepticism, no matter how valid, is just a cloak for hating on Google. I love GMail and lots of Google's products. I even like that this feature will be limited to companies that register with Google. It doesn't change the fact that those partners could be broken into and used to send out malicious emails.

Also, please don't try to insinuate that I'm against the feature. I'm not. I can stop using GMail if I ever want to. I just think everyone should consider their own security and decide how valuable it is to them based on reasonable possibilities.