494
Answer: (We are not addressing the desirability of avoiding ads, some of which are not appropriate; hopefully a religious site’s ads are appropriate.) At first, this seems to depend on the broad question of intellectual property rights. Reuven produces something of value to the masses and, due to financial considerations, attaches conditions, classically not to copy even if one legally bought the object with the content (e.g., book). Here, the question is making viewing a site’s contents conditional on allowing advertisements on your screen.
Much has been written on the topic (see articles in Techumin VI). Our opinion upholds the halachic basis for guaranteeing such abstract rights in various contexts (see Living the Halachic Process, II, J-1; Techumin XXXII: p. 233-237). In short, there are three main issues, none of which are both unanimously held and apply in all circumstances, that can forbid using someone else’s "creation" freely. 1. A form of theft even without an object being taken. 2. A requirement to pay for benefit received from another’s property (neheneh). 3. Dina d’malchuta dina – the law of the land upholds many of the creators’ claims to ownership.
Ad blocking causes great losses to many website owners. Historically, many technological innovations, including the internet itself, have enriched some and impoverished others. Upholding intellectual property rights also does not support every claim by every "owner," so let us analyze.
Let us start with #3. As far as we have seen, ad-blocking is not illegal, and we do not know if the site’s warning is legally significant. Thus, it is questionable whether dina d’malchuta will forbid using the site with ad-block.

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While we are not confident the issues above make it forbidden to use ad-blocking against the pleas of the website, we believe the owner can make it forbidden to use it. Even in a case of zeh neheneh v’zeh lo chaser, if the owner says up front that he forbids usage, it is indeed forbidden (see Shulchan Aruch, ibid.). At first glance, this restriction applies only according to those (far from unanimous) opinions that intellectual property is owned in a manner that stealing applies. However, here the owner is in a stronger halachic position because the user is connecting to a physical server, owned by them or, usually, by a web host whom he pays for their services. Therefore, usage is like using remote control to use someone’s equipment against his will, which is forbidden.
Therefore, our tentative position is that an owner can forbid you to use his site. (What it means if they do not prevent access but say it is forbidden is unclear.) We invite feedback on different elements of this new topic .

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