Again, you are connecting a sugary diet to the ill effects of sugar when really it's the fast pace people eat these sugary foods. There can be no conclusive evidence that sugar is bad because all the studies have not taken this factor into consideration
But there is more than the pace involved. There is also the amount of sugar consumed as well as the rate of absorption, which is determined by things such as the presence of fiber, fats and proteins in the stomach as well.
Sugar does have immune suppressive effects though as both sugar and vitamin C require insulin for transport. High blood sugar levels will lock of available insulin preventing the transport of vitamin C to white blood cells suppressing their activity.
Therefore, it is not a clear black and white on either side.