Unsolicited mail is a typical example that illustrates the need for ground rules. Another urgent concern is intelligence gathering by 'cookies' to track user profiles and behavior. The information is used by companies to target advertising and improve their web sites, which, however, in many cases may not necessarily be an 'evil' exercise. There are also rules needed against the posting of harmful content. This is particularly important when it comes to children and pornography.
Commercial ethics is another serious concern.
Take on-line subscriptions, for example. Some of them are very difficult to cancel, and your credit card keeps getting debited. Many users have had bad experience with this. I for one. I called American Express to stop the payment of a service subscription, but was told that they could only do so by canceling my card.