In short: The protein norm is about 1 g per kg of body weight — on average ~100 g a day. If you get your protein from full meals, you don't need protein powder. Protein powder is a protein concentrate and a supplement for shortfalls, not a replacement for food.
How much protein you really need a day
"About 1 gram of protein per kilogram of body weight. Around 100 grams is enough for muscle tissue to recover." If protein is lacking, the body starts breaking down its own muscle tissue.
When you need protein powder and when you don't
You don't need protein powder if your meals have enough protein (an omelet, meat/chicken, fish). You do need it if there's no protein in your food or a busy schedule keeps you from eating properly.
Protein powder is a supplement, not a meal replacement
"We shouldn't switch entirely to protein powder — we need fiber and whole food." You can drink protein after a workout, but an hour later you need a proper meal.
Is protein powder harmful?
"Baby formula is essentially protein at a lower concentration. If we feed a child protein, why can't we feed an adult?" The only requirement is quality: the protein should be from a reputable brand.