It's a frequently trotted-out slice of conventional wisdom, much like "DRINK A SPECIFIC AMOUNT OF WATER EVERY DAY." As long as you're having "everything in moderation" you are okay. You're golden!
Humans are obviously not very good at moderating themselves. Look around. Moderation is what got us into this mess of unhealth.
Some things you can't have in moderation. You can't have ice cream in moderation if you are dairy intolerant. You can't have gluten in moderation if you have an autoimmune thyroid disorder. Everyone knows an alcoholic can't have vodka in moderation; well a sugar addict can't have raw, unpasteurized honey in moderation. Might as well binge on jellybeans.
This is one of few topics I'm pretty "tough love" about. But it irks me when poorly-articulated, trite, conventional wisdom continues to perpetuate bewilderment around health. Someone needs to start saying something NEW. So I'm saying it:
You can't have everything in moderation. If you could well... you probably wouldn't have hired me.