I previously worked on couple of companies that flirted with the line on some of these dark patterns. As far as they go, this one is pretty benign. If I recall correctly, I was for doing this pattern. There is enough intent there (putting your whole email into the user form) that it really doesn't feel like abusing the user. That being said, me and my coworker had to fight back and refuse to build a few other dark patterns.

The real issue is the legitimate companies that take it way past dark patterns. Credit rating bureaus that scrape 100% of your data and the data of anyone you've ever been near, Facebook stalking you across the internet, etc. As far as I'm concerned, if it's okay for Facebook to do this exact dark pattern on everyone in the world, I can make a stupid directory site have a little more juice.