Yes I use an ad blocker, but as you say sites increasingly detect it and demand that I disable it for access. 
Absolutely.
Running internet sites is *VERY* expensive, and somehow needs to be funded. So assuming the site isn't selling anything, that means either:
Subscription required
Ad funded
A kind benefactor/sponsor that pays for it
So for ad funded sites, using an ad blocker means stopping that income for the website owner. Therefore I believe that website owner has every right to refuse to show the content when ad blockers are being used.
The internet isn't usable without an ad blocker, so they have themselves to blame if they don't get my business as a result.
I agree some sites are unusable due to the intrusive nature of the ads. As a rule, I choose not to use such sites.
Somebody somewhere has to pay for the stuff though, with the 3 options above being the only real options. Don't take OOF running costs as an example, because we really are a bunch of cowboys, running on a shoestring

You can't really buy a viable server for under £10k with a realistic life of 5-7yrs, and because it's monumentally moronic to have the database internet facing, that means you need a 2nd for a database. If you're stupid enough to use MySQL for a database, then you need a 3rd to use as a replica to take backups from. Then you need backups. All that has to be hosted somewhere, and due to near zero remaining capacity in UK data centres for CoLo, expect to pay £700+ per month per server - energy costs normally included, but network bandwidth usually not. Then consider that most websites taking any traffic likely need multiple front end web servers, and big sites, multiple databases, it gets massively expensive very quickly.
There still appears to be an assumption that anything on the internet should be free.