This service shouldn't exist. It breaks the very concept of email security. They're marketing it as though it's safe. Want hyperbole? Imagine Bayer marketing heroin as safe because you know, it's opt-in.
Why the hell not? Heroin from Bayer would not have the quality control issues Heroin typically has.
It only becomes problematic when you consider that the user is getting themselves into a situation that they do not fully understand and potentially cannot easily back themselves out of.
With drugs that have a high potential to cause harm, we typically force the consumer to consult a professional before allowing them to proceed. Tech is still in the era of patent medicines.
I understand the opinion, but I don't understand the sudden outrage.
LI, Google and Facebook have always wanted your third-party email credentials for Friend Finder-style features. The only difference is that this time we cannot even hope that they delete them after logging in once. Security-wise, it's all the same.