It leads to a death spiral. The closer you are to death the worse you become at combat statistics. You can't fight at your capacity, so you take more injury increasing your penalties and then die. To prevent this from happening someone must do nothing but healing. While spellcasters and other range attackers do get damaged, melee focused warriors will disproportionally suffer the consequences because it is their job to take the hits so others don't. That is why they have the highest ACs and hit points. Their reason to exist becomes a fatal flaw.