I'll try to expain my argument better:
Inertia is the property of bodies with mass wherein they maintain their momentum unless a force acts on them to change it (what we call acceleration - which can be in the direction of existing movement or not, depending on the direction that the force acts in). Newton's Laws and all that.
So imagine an aircraft flying north at 75kias in no wind. To turn it through 180deg and fly south at 75kias we have to provide an acceleration in a southerly direction capable of changing its velocity by 150knots.
Now imagine there is a 25knot tail wind. Ground speed is 100knots, with our same 75kias. To turn through 180deg and fly south, how much acceleration do we have to provide to maintain our airspeed of 75kias?
We know that after the turn our ground speed will be 50knots (75kias minus the wind speed of 25knots). So we have to accelerate the aircraft in a southerly direction by 100+50 knots = 150knots.
In both cases the change in velocity (ground speed) of the aircraft is the same. So we have accelerated it by the same amount in both cases. Which means that we have used the aerodynamics of the airplane in exactly the same way in both cases to provide the accelerating force to make the turn. So the airplane doesnt know it is flying in a wind.
If we are flying close to the ground we will see the turn as looking very different in the two cases of course..