Although I can see worrying about the effect of acidic foods (citrus, saurkraut, pickles, etc.) on the teeth, it seems the real worry is not the acid contained in foods, but the effect of the foods on the body.
Healthline sums up the situation thusly:
The pH of a food before you eat it is less important than the amount of acid or alkaline produced with digestion and metabolism of that food.
While rare, it’s possible for the urine’s pH to be too alkaline. However, in the United States, too much acid tends to be a more common problem. This is because the average diet contains more animal protein and grains but not enough fruits and vegetables.
So basically, my impression is that any food we would recommend eating on a ketogenic diet is bad for us, and most foods recommended by the current U.S. dietary guidelines are good for us. Since I have a very hard time believing that a species that evolved primarily eating meat could find meat a problem, I’ve decided that this is a bogus issue, concocted in order to provide support for the dietary guidelines.
Healthline finishes by saying
Because the body closely regulates its pH balance through a series of complicated mechanisms, following an alkaline diet is unlikely to significantly impact blood pH levels for most healthy adults.
Still, a balanced diet that includes more fruits, vegetables, dairy milk and yogurt, more plant protein sources and limits processed foods may be helpful to maintain normal acid/base balance and overall health.
Eating more fruits and vegetables and limiting animal products and high-sodium processed foods may or may not help balance pH levels within your body.
This last statement is one I would seriously challenge:
Moving toward a more plant-based eating plan has been shown to reduce the risk of chronic illness.