But the problem isn't the presence of ads. It's that the ads are served by advertising networks, that track users across multiple websites and build profiles of users.
And that the original websites have very little control over the content of the ads, which may be irrelevant or contain malware.
The ads are often animated images, sometimes with sound, which are distracting.
The ads are often deceptive ("Your computer is infected. Install this program now!") or clickbait.
Some sites don't distinguish the ads from the content, which makes it confusing.
If you want a blast from the past, disable the popup blocker on your web browser and see how many sites still fill your screen with intrusive popups and notifications.
Also, people have used video recordings of live television to skip commercials. Some devices even have a commercial skip function. Or people just mute the television while commercials are playing. If this is acceptable, then why not block ads on websites?