The problem is, some (poorly written) websites don't work without the ads. Sometime you just don't care and close the tab, but sometimes you don't have a choice and in that case disabling the host file is a bit of a hassle. I prefer simple extensions like uBlock Origin which do all the work for me and that I can enable/disable as needed.
I've seen a lot of websites that don't work without scripts in my time, but never one that doesn't work without ads.
It would be possible to make one like that by hosting your content and your ads on the same domain, that would trip up naive hostfile blockers, but of course if companies were doing this quite a lot of people who habitually block ads wouldn't mind them doing so, since one of the key complaints against ads is data harvesting by third party ad providers.
I've seen websites being broken because they load some ad js, and when it fails it throws a js error which prevent the rest of the script from working. Also some websites wrap their outside urls in tracking urls, and these break as well with ad blockers.
The ones that explicitly detect adblockers and refuse to show content are usually sites that deal with more... shady material. When I need something from one of those, I find that Google's text-only cache is often enough to get the content, and if not it's really a question of how much the content is worth to me --- the back button is only a click away. What I won't do is enable JS, however; I'd sooner reverse-engineer the script and figure out how to get the content it loads than let dubious arbitrary code run.
But like I said, the back button is effortless and if your content is not rare, I'm going elsewhere.
