Because it means that a business (as in, facebook) knows too much about you. It's extremely invasive privacy-wise. Things that could happen: * Micro-targeting

Because it means that a business (as in, facebook) knows too much about you. It's extremely invasive privacy-wise. Things that could happen: * Micro-targeting for political advertisements (pretty bad for democracy) * Dynamic pricing based on demographics (you can afford it, so you pay more) * Insurance knowing too much about you (rejections based on your health, ensuring parts of the population won't be able to get good insurance) * And just the fact that too much information being public can be harmful (blackmail, scams, etc) * etc..