Fair enough, but the ethical thing is for Google to exclude bing.com from the clickstream analysis, and I hope they have.

The big search engines are large enough to show up clearly in any of their competitors statistics (and there are always human teams monitoring the automated process) and should specifically exclude data from their competitors.

For Google to use Bing clickstream or vice versa also perpetuates a vicious circle where bad results from one search engines will spread among the others.

Bing either hasn't acted ethically, or hasn't though through the consequences of absorbing clickstreams of competitors' sites.