How can the principle of "no harm and no causing of harm" be reconciled with the fact that taking medicine is permissible but not obligatory?

Seeking medical treatment is permissible according to the majority of scholars, and it is recommended by the Shafi'is and some Hanbalis. Some scholars have held that seeking medical treatment becomes obligatory if one fears death without it, citing the principle "no harm [shall be inflicted] and no harm [shall be reciprocated]," such as amputating a decaying limb to prevent the spread of disease. Thus, the principle "no harm" pertains to obligatory treatment, not to treatment in general.