It's that targeted ads are meant to manipulate your decision making. In order to do that, you're tracked, yes. You can prevent them from manipulating your decisions (put your blinders/Adblock on), which is really great even if you can't prevent them from tracking you.
Targeted ads are insidious - as natrius says, they prey on your psychology. By comparison, non-targeted ads are generally just an eyesore.
Psychologists know that humans have certain exploitable weaknesses. I mean, think about any relationship. You become vulnerable when you expose yourself, and so a person has to earn your trust such that you expose yourself to them.
Today, advertisers have made you vulnerable without actually earning your trust. You could argue that "by using Facebook you're saying you trust them," and you'd be right... If humans all had the capability and willpower to understand systems as complex as ad targeting... One of our worst exploitable vulnerabilities.
Put another way, I would say that it's ethical for a team of scientists to sit down and interview you about everything you love/fear/want/need for the purpose of helping you to find more people like yourself so you feel less lonely. I would say that it's unethical for those scientists to radio down the street as soon as you walk out the door to tell street vendors to start hawking goods that play at your insecurities.
Not all advertising is based on exploiting people, but the most effective types are!