This is one of those difficult spaces where the actual player, and the player character, blur and also tend to be at odds. What you describe with people being afraid to go fight a zombie with just a pipe or the like? It is exactly what happens to new players already, faced with dangerous enemies they don’t know how to handle. They will react with fear to preserve their characters life, or overconfidence that leads to death if they fail to accurately judge the enemy.
The problem is that once a player gets experienced, that fear goes away. I know very, very well what can and cannot be taken on with certain gear and skills, but its player knowledge, not character knowledge. A very common version of this is discovering kiting through windows/doors, or kiting with reach weapons, stuff the player knows makes many enemies much easier to take down even with inferior gear.
When you try to systematize it to represent something the character is feeling, you end up with a major problem. If the player is new, and afraid, but the character is not, then the player starts to use the characters own reactions to judge their abilities - Which easily backfires, when the player character expresses confidence in a situation that gets them absolutely killed because the player didn’t know how to handle it the way the fear system expected when it rated if the character should be scared.
It gets worse when the player is experienced, because the player knows ways to do things that the fear system most likely won’t account for. All you end up doing is annoying the experienced player with seemingly artificial stat reductions that they can’t really do anything to mitigate, based on a system that will inevitably feel arbitrary.
The actual solution to this isn’t to try and put a system in place to ‘punish’ the player for fighting scary things by placing artificial handicaps on them, but to actually make the enemies in question dangerous enough that the player themselves has fear reactions regardless of skill.
I do believe that we will march indirectly towards addressing the fearlessness of players with the coming health and wounds system changes, where injury goes from simple HP and more towards meaningful measurable damage, allowing more varied consequences that aren’t just immediately “Player Dies”. Right now, a really scary enemy is only really scary because they can obliterate HP, and then its not a really interesting enemy. If the enemy can instead deal a harsh wound that is survivable, but has long term consequences. Then it becomes a matter of designing the right wounds and consequences for enemies to become feared even for experienced players. Not because of immediate ability to kill you, but the fact that engaging them carelessly or even getting a bit unluckly could impact your save for much longer than the usual “Sleep it off, or you’re dead” mix.