Bergqvist says, "It is never a good idea to take off with a tailwind." Never? Really? Are you sure? What about a sloping runway where the downhill gradient more than offsets the effects of the tailwind? What about an uphill takeoff where the runway gradient more than offsets the effects of the headwind? What about a runway in rugged terrain where a takeoff into the wind would point you toward terrain that you can't outclimb?
It is important to know the effect(s) of the wind on your takeoff roll regardless of whether the wind is coming from in front of you or behind you, and to monitor your aircraft's performance during your takeoff roll. An old rule of thumb is 'at least 3/4 of takeoff speed in 1/2 of the runway or abort'. (While you're at it, don't forget to factor in the effect(s) of the runway surface - pavement, firm turf, long grass, etc.)
"Never" and "always" should be used carefully. There are times when they apply, but often "seldom" or "usually" is a better choice.