Interestingly, if I use a 'browser' like wget I've basically transformed that computer program into what amounts to a non-program. Wget doesn't even have the facilities to run that Javascript. So it is possible that using wget in Germany is illegal?

I guess legally at some point you have to either execute or "decompile" that non-program, and the same violation would apply if you remove the ads ("violation of its exclusive right of modification").

The complex part here is that they don't sue you as the consumer, or consider the execution/decompilation illegal, but AdBlock as the tool which removes the unwanted content from it.

In that interpretation the only legal way to consume the content is completely unmodified, and the seller built a business-model based on adding something that only he benefits from. Weird scenario...

Given that someone was sued for opening the developer tools on a website, using wget would presumably constitute a death sentence.