That would be like saying a service that blacked out the ads in news papers is theft, its completely rubbish. Plus educate yourself on the definition of theft:
"theft is the taking of another person's property without that person's permission or consent with the intent to deprive the rightful owner of it."
At best its unauthorized modification of a creative work without distributing it, which is not illegal and never will be.
Don't know why parent comment was killed when the article contains a similar assertion (the other way). While not a lot is gained by using loaded words like "theft", it is a simple fact that using ad blockers causes the owners of many of the sites that you visit to receive less revenue than they would otherwise. One can argue that one is perfectly justified in doing this (e.g. many typical examples of this are included below), but one can not truthfully say that they are not taking money away from the sites they visit. (Yes I know about PPC ads and how you never click them. Other than AdSense, the vast majority of advertising out there is sold on a CPM basis.)
That's present in uBlock too, despite some fairly unintuitive UI - the big green power icon isn't a full disable for the extension, it disables it for the current site only.
"theft is the taking of another person's property without that person's permission or consent with the intent to deprive the rightful owner of it."
At best its unauthorized modification of a creative work without distributing it, which is not illegal and never will be.