Why can we say that modesty is unhealthy?

The meaning is different. Modesty: It means not being complacent or arrogant. Modesty makes people progress. Health means that all physiological functions of people are normal, and there are no diseases or defects. The two have different meanings and cannot be confused. For example, respect is the embodiment of personality, respect is self-modesty, and respect is the foundation of social harmony.