Third, you can't force people to use the correct semantics. They'll use them wrong on purpose for fun and profit. Mark some disturbing content as wholesome, mark it as whatever is popular at the moment to get it in front of more eyeballs, mark it as something only tangentially related in the hope there's a cross over of market, mark it wrong because they don't actually know better.
Yes, I think this is the biggest issue. Since many websites are funded by advertising, they do not want people to be able to extract data from their pages, they want people to "visit" the site and view the ads.
Also, rights. People "own" things like sports fixture lists... they don't want you extracting that data without paying to use it.
The semantic web could be perfect technically, but it was never going to apply to content that people were attempting to "monetise"... which seems to be most of the web's content.
I don’t really understand this argument, because there already are lies published on the internet. What difference does it make if those lies are published in a standardized machine readable format or not?
A human-targeted web structure that contains some lies is still useful for humans because humans can filter out those lies with somewhat satisfactory efficiency.
A machine-targeted web structure that contains some lies is not useful for machines because they can't filter out those lies yet. It might become useful when they can (but that might be a hard-AI problem), but it's simply not usable until that point.
We as humans have a lot of intuitive tools for knowing whether a source of data is trustworthy. AI could possibly approach this ability given enough training... we'd need to do something like add a "trust" score to every node in the graph.
