A double edged sword is what we've got. But more than not, it is the owner of any website to decide whether or not they can afford to pay "X" amount of dollars per year for web hosting space in order to offer a "service". But you see, that right there is the catch. If you are offering a "service", then it is a business.
A business as such has the right to ASK their viewership for a membership fee. The Mac-Forums ASKS for a fee per year which if you know anything about the costs of maintaining such a service, is more than enough to cover said maintenance. Ads are supplemental and serve two purposes. One, they do bring in some revenue, especially if the user base is large enough. It's simply a matter of chance and ratios. Secondly, ads are an annoyance and might even sway some towards paying a yearly fee in order to get rid of them!
But please stop getting things twisted. The internet as you know it is NOT free, as others have already stated. You do pay for it. Everyone does. And it's a level playing field. If you can not afford to pay for server space, then don't think that you have the right to force ads on people in order to provide your oh-so special services!
Many internet services are subsidized by their share holders (Google, Facebook etc..) and originally had very sizeable financial backings in order to get started. Business is business and that is fine, but to say that it is stealing by blocking ads is ridiculous. If a website owner feels that they are providing a legit service that others can not do without, then they can absolutely ask for a monthly or yearly membership fee.
The website owner can also restrict the type of access that a person has to their site if they're not a "member". The Mac-Forums does this, and many other sites do this as well. It's called the perks of membership, and if done right, can be a LOT more effective than trying to generate revenue from ads. But then, the site has to have content with real value. This can not be said about most of the sites which kill you with ads.
Doug