Title: More Dangerous, Less Wise
Source: The Hobbit, Unfinished Tales (The Quest of Erebor), LoTR Appendices
Characters: Thranduil, Legolas
Disclaimer: Middle-earth belongs to Tolkien and his heirs: I wander there for fun, not profit
“The Wise – hah! – deign to assault Dol Guldur.” Thranduil's penknife rasps furiously at his quill. “No matter that we have battled the Darkness unregarded for an Age; now that it suits their purposes... Oh, I do not blame Mithrandir; he has urged them to this for yeni, I know. And Radagast loves too greatly bird and beast to notice overmuch the politics of Men or Elves. But Curunir... I do not trust.”
“Imladris, Lothlórien, Mithlond?” Thranduil's bitter laugh surprises his son. “Fear not, Legolas. They are safe enough.... all three.”
The White Council met in total four times (that we know of) during the Third Age, and Gandalf had been urging an attack on Dol Guldur since at least 2851, opposed for much of that time by Saruman. I know people also debate whether Thranduil is a member of the White Council (given that Elrond, Galadriel and Cirdan are known in canon to be so); but the very fact that (if Thranduil is indeed the Elven-King of The Hobbit) he is feasting/dealing with the Dwarves in Mirkwood at almost exactly the time the Council are assaulting Dol Guldur at last, suggests that he isn't. Which would all feed in to my head-canon of his chip on the shoulder/feeling of being sidelined as a non-Ringbearer by the so-called Wise, while he gets on with keeping back the Shadow year in and year out...