If ad blocking become widespread, you will start seeing the following:
- Some content will simply disappear. No ad revenue means no money to pay for web hosting. A lot of smaller sites will disappear, especially for those who do not know how to monetize their content some other way.
- Other content will be placed behind a paywall. All your news websites with professional staffs will be forced, from an economic perspective, to charge subscriptions again. You might get some content for free, like the Wall Street Journal, but you will be forced to pay if you want to read more.
- The quality and amount of free content will decline and there will be more paid content. Authors and publishers will look at their options, and decide that free content is no longer a viable way to make a living, and start focusing on content they can charge for. Poor quality content may still exist, but those sites never last as an ad revenue source because they are low quality.
- Some websites will start tailoring their content to sell you something. So they may still give you free content, with the intention to persuade you to buy their paid content, or buy their product or service.
- Other websites will have donation drives and ask for you to donate so they can keep providing their content for free. The biggest example of this is Wikipedia who depends on millions of dollars or donations. Smaller websites aren't necessarily going to get the same level of donations.
So, on a small scale, ad blockers are probably okay. But on a large scale, the free internet as we know it will change drastically.
It's simple economics. Servers cost money, electricity costs money, internet access costs money, a content creator's time costs money. Someone must pay somehow or a huge chunk of that free content goes away.