While adblockers make some people quite happy, there are others that consider them immoral; see for example this tweet. Let's set aside the security issues and other counter-arguments to note something important: much as in another case, it's extremely disingenuous to discuss morality here without mentioning the blatant amorality of advertising on the web itself. To put it simply, the ad industry and its supporters are coming to the table with extremely unclean hands.

By and large, the story of web advertising and ad companies and networks is a story of organizations aggressively and unapologetically tracking and intruding on people for years. At every turn web advertisers have done their best to obtain more information on more people, to mine this for as much creepy insight as they could, make as much money from it as possible, and never ever ask people for permission or even inform them. At every turn, the ad industry's view has been that if they could get away with something it was all good, especially if it was legal. Morality has never entered the picture.

The ad industry has spent years cultivating a 'fuck you' attitude where they would do everything that was within their technical capabilities to spy on people and shovel ads on top of them. To now suddenly be concerned about the 'morality' of what other people do is the height of hypocrisy. The ad industry has lived by the sword of 'technical capabilities are all that matters' (to the detriment of basically everyone else on the Internet), so it's only fair that they may now die on that sword, like it or not. Adblockers are possible, so by the ad industry's own conduct they're allowed.

(Since the ad industry has no morality it of course doesn't care about its own hypocrisy here; it will bleat whatever bleatings stand some chance of keeping its exploitative business model from collapsing. But bystanders should be listening to these bleatings with a full understanding.)