Society would need to determine resource prices. The idea of scarcity is based upon unlimited wants and limited resources. Resources are scarce. Consumers like a variety of goods. Tradeoffs promote socioeconomic goals.
Tradeoffs increase efficiency.
Opportunity costs are always associated with tradeoffs. Opportunity costs are sometimes associated with tradeoffs. Opportunity costs are never associated with tradeoffs. Opportunity costs are the opposite of tradeoffs. The opportunity cost of dieting is the same for everyone.