It's also irrelevant. Whether the users know or not, whether they gave permission or not, Bing is still receiving *and using* direct search data from another search engine! The click-through is monitoring two pieces of data and then providing that back to Bing - the search term entered into Google, and the page the user goes to after the results page is returned.
Let's go back here a bit. Google builds up it's search results by a variety of methods, but mainly through:
* Web crawling and categorising web sites.
* Recoding what results people pick whne they do a search on google.
This is more or less how we expect every search engine to work. The success of the engine hinges on the methods and algorithms used to piece all that data together in a meaningful way, thus providing useful results that keep us coming back for our search needs.
In this case, Bing has, in essence, spied on another search engine. It's taken this data deliberately (the tool bar or the server that processes the data that is monitoring the end user would need to be aware of how a search term is entered for google. It has to have been coded for this).
The fact that Google did this deliberately is irrelevant to the simple, plain fact that Bing is indeed deliberately recording Google search terms and results. And they aren't even checking such data against their own database in any meaningful way. If their own web crawling and search data was halfway competent it would have identified that the search terms didn't match the results in any meaningful way - from a simple text index to a multi-faceted category/semantic classification approach, this was a nonsense phrase unassociated with the page in question.
Are you arguing that the way this data is obtained means it's not stealing? It's only the difference between looking for something yourself or asking someone else to do the looking for you. Either way, they are relying on the results of other search engines to bolster or ammend their own. There's a degree of dishonesty and desperation about that.