Conceptually I'm ok with there being a chance of infection from any wound, the problem is the combat is a bit too glitchy to enforce that heavy a penalty. It's impossible in any video game to give you the level of control over a character you would have in real life (no game to date is capable of allowing you to independently control each limb simultaneously, which significantly reduces your combat effectiveness compared to real life). For that reason, you have to curb the damage penalty and project zomboid combat is even a bit "wonky" and limited compared to other games. Not to mention the fact that most people can't use guns because they are so useless at lower level while still aggroing every zombie around and they are so rare that you usually can't find enough ammo to level up to where guns are useful before you die.