Others have and will make a much better case for why this is so. While it cannot be optimized, the benefit of biological characteristics is its ability to learn. A forest can adapt to seasonal forest fires, a child develops antibodies after they catch the chicken pox. In either case, it is the temporary trauma which breeds long-term resistance. A forest which did not evolve fire resistant seeds or an adult who was never exposed to chicken pox runs a far greater risk.
Advertising is a new factor introduced in the environment of the Internet.
The Internet must learn how to deal with advertising. True, it is no fun when some bozo sends out an unsolicited ad. True, the following flames and discussions are not an efficient use of bandwidth and time. But this process is necessary and will continue with many other issues. What's more it is this very inneficiency that makes the Internet so strong.