Over 140k virus species in the human gut, half of which are new to science
Hypothesis: general anti-virals (i.e. something that kills most viruses, rather than being fine-tuned to a specific virus) will have the unintended consequence of killing viruses which prey on bacteria in our gut microbiome.  That, in turn, will alter the balance of bacteria in our gut, leading to (slow-to-appear) major health issues.  All somewhat similar to the autoimmune and allergic issues resulting from overuse of antibiotics.Just a hypothesis.  But the number of viruses in the gut, the vast majority of which we know nothing about, does reveal an awful lot of room for unintended consequences.