Wikipedia has never used their near monopoly to juice neighboring businesses.

Google has, for example:

* Used search to promote their yelp alternative (this is a big part of the EU antitrust case);

* used search to promote chrome;

* used search to attempt to compete with fb (having google+ bumped location in search results / gave you better display in search results)

There is no line. The state shouldnt intervene in business as much as possible. But search is at the core of the internet and an increasingly connected society. Its too important to be allowed in the hands of a single company.

Wikipedia doesnt own 90% of the 'knowledge base' market - maybe not even 9%. If it did, then there might be a case for it too.