Ads make pages load slower. Ads on mobile browsers make the text jump around while I'm trying to read it. Ads put giant pop-ups over the text that I'm trying to read. Ads start playing loud music, or flash.
The problem isn't ads, it's a lack of bounds about what ads can and can not do.
The web ran fine for years with ad-blockers as a niche; but ad-blockers only got popular when the ads themselves overstepped their bounds and became too intrusive.
I'd be much happier if ads were reasonable and I didn't feel like I needed an ad-blocker just to view the %$#%@ website.