That due to people not being informed and jumping to conclusions. There is a condition known as diabetic ketoacidosis in which the blood pH becomes too acidic. But this is NOT due just to the presence of ketones. When your blood has plenty of glucose in it to meet your energy needs but you don't have enough insulin to get that glucose into the cells where it is needed then your body tries to dump the sugars in the urine, which also dumps key electrolytes such as sodium and potassium and also leads to severe dehydration. The body then turns to its other fuel source and starts turning fat into ketone bodies, which are acidic. The body has buffering mechanisms to keep the blood pH within limits, but these are quickly overwhelmed by the other things that are going on and the blood pH falls to dangerous levels. But this process basically requires two things at the same time -- very high blood sugar levels and very high blood ketone levels. If you only have one or the other, there's little danger.

Nutritional ketosis is the lowering of blood sugar levels through dietary choices (very little carbs, for the most part) so that, once again, the body turns to fat and ketone bodies as its fuel source. But in the absence of high blood glucose and the other things that go along with it, the body is more than capable of buffering the blood pH adequately.