There is no physiological reason for eating 80% healthy and 20% unhealthy. There only possible reason for such a rule is psychological. It is a helper rule for dieting instead of a commitment to a healthy lifestyle. As most of us know, dieting is a war that cannot be won. 20% becomes 25% becomes 45% until you get disgusted and then cycle back creating a dieting yo yo.
But all of this goes to someone who is concerned about their health. If you are eating bacon, then you don't care about a healthy lifestyle or diet. Eating highly processed meat stuffed with nitrates, fat, and salt is not good for you. Duh. Yet you eat it anyhow. Recognize the choice you have made.