In general, people whose conflict resolution strategy is to punch the other person aren’t very good society members. If a pathogen somehow weakened the human body so dramatically that everyone could kill anyone else with a single punch, what would keep society from collapsing as power is placed into the hands of people who are, essentially, savages? People with the least morals are suddenly the most powerful people on the planet. What could keep them from taking over?
I’m trying to avoid the whole “everyone wears football pads around all the time” answer. I’m looking for societal changes, not technological solutions.
This weakness is fairly specific- it makes humans frail, not necessarily feeble. An alternative mental model would be “everyone is given enough strength via superserum to kill anyone else via one punch”. Similarly, one could imagine that everyone is given the power to kill with a single glance. The mechanism isn’t that important to me, it’s more about the effects of people with the least restraint suddenly being more likely to be in charge.
Society-wide taboos on punching people are also not acceptable answers. We’re talking about people who are already unafraid to break the law, they just know they won’t get away with it.