In "The Best of Both Worlds, Part 2", when it seems all is lost, as a last resort, Riker decides he is going to ram the Borg at maximum warp in a bid to stop them reaching Earth, which would of course destroy the Enterprise.
We never find out if it would have worked, and yes it was an act of despair, but the question remains: why did Starfleet not just use unmanned ships as weapons, or even just strap a huge ship-sized missile to a warp drive?