That's only for economic profit. Normal profit remains even when economic profit is driven to zero:

https://www.investopedia.com/terms/n/normal_profit.asp

"Economic profit is the profit an entity achieves after accounting for both explicit and implicit costs.

Economic Profit = Revenues - Explicit costs – Implicit costs

Normal profit occurs when economic profit is zero or alternatively when revenues equal explicit and implicit costs.

Total Revenue - Explicit Cost - Implicit Cost = 0

or

Total Revenue = Explicit + Implicit Costs"

In a perfect system, I wouldn't pay a penny more than your total cost. Capitalist extraction can only occur because we pretend it's not an exploitation of unequal knowledge.

No, profit is just and economically rational compensation to the investor. Without it, the opportunity cost and risk of saving and investing, respectively, is not compensated for.

I think you are thinking of competition. Free makrets and competition are not the same, although they are related. In highly competitive markets, there is no profit; this has happened many times in history. Usually the result is that many sellers leave that market. In modern industrial policy, policy makers will seek to prevent "excecive competition" because it inhibits growth. This idea is related to what GP was saying.