My opinion is that excessive sun applied to skin not used to receiving excessive sun and causing burning can lead to skin cancer. If one is in the sun everyday, as our ancestors were for thousands of years, the skin is able to deal with the sun and actually receive healthful benefits from it. If we sit in front of a computer for 200 days then go stand in the sun for hours and get burned we will get cancer.. My conclusion.
1. The ingeredients in sun block are harmful, however possibly not as harmful as receiving a burn.
2. If we slowly get ourselves used to the sun, and don't be stupid, not using sun block is a better choice.