Many aircraft have rudder limiting units to keep rudder movement to a small amount at higher airspeeds. For instance the ERJ-135/140/145, ATR-72, Saab 340B. This is because at higher airspeeds, a full rudder movement could cause structural damage. I'm sure that many other aircraft have the same feature.
The above examples work in one of two ways. In the ERJ, there are two rudders, both combined. It is basically taking the whole rudder, and cutting it in two longways. At higher speeds, one of the rudders is locked, restricting rudder deflection angle.
In the ATR and Saab, the rudder has a limiting device, that limits deflection angle of the whole rudder (not split). This is also activated at higher speeds.
When I was working at Trans States, we had an ATR-72 that had a malfunction of the rudder limiting unit. It had to hold until the problem was fixed, because as the captain explained "if we get above a certain speed and kick that rudder in the event of an engine failure, we could bend the fuselage. It's just too long."
I have to question whether the rudder problem on the A300 was truly rudder movements as stated. From the procedures I have had experience with (B737, B757/B767), yaw damper is engaged before start/before takeoff. This limits rudder movement, and has "automatic" (in a sense) movement for rudder changes. If the crew had this engaged, and were below 250 knots (maybe lower), how could they have overstressed the vertical stabilizer if it was in good condition? Even without yaw damper, it would be some nasty inputs to do that.
The other day I was flying a single engine ILS with a nasty crosswind and windshear, and was fighting the plane the whole time (B737). At times I was putting in a lot of rudder when the shear hit, and we didn't have problems. Of course it is a simulator. But what I'm getting at is directional control was maintained, and the inputs were not so drastic as to cause structural failure.
IMHO, I don't think that the American A300 crash in JFK was caused by pilot inputs alone.
Am I worried? Not really. I figure if it is going to happen such as it did in JFK, well there might not be much I can do about it. I will fight the plane to the end trying to save myself, my crew, and my passengers, but if it is structural, what can you really do?