Well, a lot of people use their computer to purchase things. How do people know what to purchase? Ads! Therefore more ads = more knowledge about what to purchase and results in a better user experience QED /s.
Take Uber, for example. It's apparently a popular ride-sharing service, which I've only heard of recently due to a bunch of articles about them getting into trouble with the law. So how did that service get to be so popular to begin with? How did people first hear of them? I'm guessing that there were lots of banner ads for them all over the web, which I've never seen.
Of course, my curiosity as to what goods and services I might be missing out on is not strong enough to cause me to turn off Adblock, because good lord, the web user experience is horrible without it.