A closer analogy would be washing your hands without soap. Yes, you get them wet, but are they really clean?
I think people forget that washing clothes is a science, and skimping on agitation, detergent or water temp will have an effect. (note: FS doesn't help cleaning one bit, but can cut static cling).
You need good warm water (something above 110F is recommended...consider body temp is ~98.6 and dirt and oils are being transferred to those clothes with fibers around those temps). That warm water opens up those fibers so the surfacants in the detergent can get at the trapped soil. The hot water also helps activate the enzymes (remember, we lost out phosphates) so that they can break down the oils and fats. The mechanical action allows these soils to be extracted. With a traditional top load machine, the fats and oils rise to the surface and are spun out on rinse (again, those surfacants come to the rescue).
Obviously, there are cold water detergents (and have been for 50+ years), and these do have specially designed enzymes that activate at lower temps, but there are tradeoffs in washing ability, and I suspect additional optical brighteners have been added. Extended agitation time would help compensate here, but only to a point.
Back to the hand washing analogy, what's most effective? Holding them in water without rubbing? Applying soap and rubbing, but no water? Or the combination of all three?