Final answer:
Viruses are destructive because they can cause damage to the cells they infect, leading to negative effects such as data corruption and slowed down computer performance.
Step-by-step explanation:
Viruses are considered destructive because they can cause damage to the cells they infect. This damage can lead to various negative effects, such as slowing down computer performance or causing data corruption. Viruses do not improve system security or enhance file organization. Instead, they disrupt normal cellular processes and can harm the host organism.