imagine that you want to end humanity in a virtual world. Use this internet connection to that virtual world.
COVID only killed under 1% or so of those exposed. But there are plenty of diseases with far higher mortality. What makes you think we couldn't make something as deadly as rabies (kills 99%+ of those who get symptoms) but as transmissible as the common cold?
Given that "nearly everyone" was exposed, that value is an order of magnitude too high, should you compare it with how many died the years before covid and during (but before vaccination was generally available) as fraction of the presumably exposed population. All of this is public data, but it probably makes sense to exclude countries with notoriously bad data such as China and India.
Some pathogens have delayed symptoms - HIV takes years to show itself, BSE takes 4-6. A fast spreading aerosol version of something like this would be… bad.
Someone is gonna do gain of function research on pathogens, and it's pretty rapidly becoming something in reach of determined hobbyists, let alone rogue states.
I think I'd prefer we understand what's possible, how pathogens vary in deadliness, how they might be modified by less friendly actors, etc., and I'd hope it's not being done in a cavalier fashion with regards to safety.