Aluminum is suspected of being the cause of some illnesses such as Alzheimer's but this has never been proven. It was an assumption based on the presence of aluminum in some Alzheimer's patients. But presence of does not mean cause of. So the toxicity of aluminum is not really known.
There is also a question of stability of the silica-aluminum complex. Silica is used to bind and remove aluminum from the body. So it is believed that the aluminum in the DE is not an issue since it is tightly bound to the aluminum. I personally am not that worried about the aluminum in the DE for that reason and we are going to get aluminum in our diets from many other sources including plants that pick it up from the soil. Being that we are not all dead or have aluminum toxicity the silica in the plants among other compounds must be doing a pretty good job of protecting us.