Our bodies are acid forming by nature... any movement produces acid waste... lactic acid. If the body does not have enough alkaline minerals to neutralize the acid produced we get sore.
There are other examples, but the issue really is about balance. As we are acid producing by function, we need to eat a primarily alkaline diet to be at our best.
Sure we can live a long time in an acidic state, but then we start talking about quality of life.