The Nazis spent a lot of time acquiring factual information about the Katyn massacre, it's worth knowing the motives.
Assange has certainly played with outright lies e.g. Seth Rich.
Most of WikiLeaks output as far as I'm aware is mostly truthful to what was given to them, with the caveat that they are telling a story (e.g. bellingcat have no issues finding dirt on Russians, WikiLeaks don't).
They are also very happy to cause collateral damage of their own, IIRC they're very happy to leak personal details & CC numbers of people associated with those they dislike (iirc it was democratic donors in some US state, the data was leaked unredacted).