Why shouldn't I ask my customers to provide feedback on Internet? A business must encourage their customers to spread good word by various channels like social

Why shouldn't I ask my customers to provide feedback on Internet? A business must encourage their customers to spread good word by various channels like social media, word of mouth, blogs, links, reviews, invite friends etc. This practice has existing long before Internet, and internet has made it easier than ever. Google is essentially telling us not to ask our customers to evangelize for us. Why such hypocrisy? How about the invites system Google uses for many products including Gmail where users are encouraged and incentivized to invite friends. According to Google's terms if I link to my Dropbox referral link on my blog, Dropbox should be penalized for it because they incentivize users to do that. The internet should not work according to Google's algorithm and policies, it should be the other way around.