Hmm, I don't know. I'm pretty sure our default search engine right now is
Google. While I don't have any data to back this up, I imagine the software
behind DuckDuckGo is "freer" than that behind the Google search engine.
On the other hand, Trisquel is a fully free operating system. You're
completely right in saying that we shouldn't be recommending the use of
non-free software, even if it is a web service like it is in this case.
But on the other other hand (that's three hands, now), people need to do web
searches. It's one of the primary things people do on the web. Is there
actually a fully free search engine out there? I'd like to hear about it if
there is.
Then again, Google is synonymous with web searching to many people.
Providing them with something like DuckDuckGo, which they've probably never
heard of, could be confusing and off-putting.
Like I said, I don't know. This certainly is a tricky situation.