He never said that refining medicine was bad. He only meant that it was not good for her to continuously refine medicine.
"Master, you're very good at refining medicine. Others can refine one batch of medicinal pills, but you can refine three batches. Moreover, your level of medicine refinement increases very quickly.
"However, this is also what I'm worried about.
"Your medicine refinement level has increased so quickly, but your Original Soul energy hasn't increased much. I'm worried this will cause great harm to your body. You may be burning your life force to refine medicine."
Others could refine as many pills as they had Original Soul energy, but what about his master?
Her Original Soul energy level was far lower than that of her medicine refinement. If this continued, her body would eventually have problems. He had reason to be concerned.