I don't think we have any idea yet in the big picture. Is ad revenue the right way to support web sites? Are the costs of running web sites small enough so that they can be born as an incidental cost? Should your internet provider be charging more and then awarding some fraction of that to the sites you visit? Dunno. Society is complex; one could make some guesses using game theory, economics, and so on, but mostly we'll just have to wait and see how it turns out.
When it comes to an individual site, if advertisers get zero click-throughs they'll stop advertising there (or by some means the site will fail to earn money from having ads). Blocking ads is not necessarily any worse than letting them through but ignoring them. The bottom line is that usually merchandise needs to be sold, eventually, and if that never happens, careful advertisers will stop doing it. If your patronage is a substantial part of what is keeping a site afloat (very unlikely), then not being influenced by ads to detectably change your buying preferences is perhaps shooting yourself in the foot.
Otherwise, it's a classic case of the tragedy of the commons: there is a public good, it is supported by some, and you're not doing your part. You might also go do a potluck dinner and not bring anything; use roads and libraries and such and not pay taxes; cut down trees for your fireplace and not replant them (and not own the land they grow on); or any number of other things where you consume a resource that you and others rely upon without replenishing that resource in any way. Most ethical systems frown upon this, though the depth of sanction depends on the details. It's a clear violation of the Categorical Imperative, for example, and you wouldn't make this a rule in rule-based utilitarianism since everyone would probably end up worse off if everyone followed that rule. A few systems have genuine trouble with tragedy of the commons; ordinary utilitarianism is one of these, as it has no mechanism by which individuals can recognize collective harm and avoid it (e.g. it's better for me to not read ads, but if nobody reads ads and there's no web site, we're all worse off than we would be if we had the site and read ads).
In summary: this is typically not considered moral behavior, but as the harm is miniscule, the degree of sanction is, in most systems, quite mild. ("Tsk tsk!") There may be no sanction at all if e.g. you are not the intended audience so the ads don't really apply to you, but the incidental cost of you increasing network traffic a little is so miniscule as to be irrelevant. (Basically all utilitarian systems would say, "Oh, no worries then," while you'd still be on the wrong side of the Categorical Imperative unless you could very carefully craft your general maxim; rules-lawyering maxims is generally not considered to be good form e.g. because you're likely to suffer from bias due to self-interest.)