If a man will begin with certainties, he shall end in doubts, but if he will be content to begin with doubts, he shall end in certainties. - Francis Bacon
Everything in project work is uncertainty. Estimating is required to discover the extent of the range of these uncertainties, the impacts of the uncertainties on cost, schedule, and the performance of the products or services.
To suggest decisions can be made in the presence of these uncertainties without knowledge of the future outcomes and the cost of achieving these outcomes, or deciding between alternatives with future outcomes ignores completely the notion of uncertainty and microeconomics of decision making in the presence of these uncertainties.