It's for content farms only. Not unpopular sites, religions, etc. You think Google is going to remove whitehouse.gov from all results if enough of the world votes to block it?
I'd say it's for blocking things that are objectively farmed or splogs, not sites with correct information that happens to be subjectively poor quality or out of date. It's for improving the index, not cleansing the internet.
I'm simply concerned by the fact that they consistently rank highly on Google, which leads to the spread of incorrect information.
It is one of the more complete reference websites, but anything you learn there should be checked elsewhere.
Looking at the list on w3fools, it seems a little pedantic (aka nitpicky).
- efreedom.com
- experts-exchange.com