You are getting a top-class VSTi for free, and all that is asked is that you register the same way all other Steinberg customers do. You can easily opt out of the newsletter (sent infrequently) which is nevertheless one of the best ways to stay informed about Steinberg products. We all know what spam is, but I personally have never received any email from Steinberg that I would classify as spam.
While I feel just as strongly about giving up any personal information, there has to be some exchange of communication to do business at all; for example, you gave an email address in order to join this forum in the first place. If you feel it is illegal, then you should reference what law you feel is being broken and I’m sure Steinberg would be very interested to address any such issues.
Finally, I think Steinberg’s approach overall is fairly balanced, certainly compared to companies who, for example, require one to sign up to Facebook (and “like” them!) in order to enter a competition.