Every day we have data collected on us and sold to advertising firms and other companies to show our interest in a certain product or brand. This information is collected on us regardless of whether we want them to or not. Our privacy is being violated and most aren't aware of it.
This is a feature that should be an opt in and if your aren't made glaringly aware of it, it shouldn't happen. By allowing users to opt in they can receive personalized advertisement and things of that nature, if someone doesn't want their information tracked it shouldn't be as difficult to remove yourself from the data collection mechanism a company is using.