However, they're not doing anything harmful with your information, and they're just addressing that information to you.
Many iPhone apps do this with your address phone book as well - such as Viber.
I'm not too sure what's going on in the backend system, but I doubt they're able to look through your whole contact list. In any case, turn off the Push notifications if you don't enjoy them.
Where it gets harmful is when they use your information for something else - then I agree with you. If the information is meant to serve your needs, it should be fine.