> Water alone doesn’t do a very good job of removing sweat

Citation needed? Sweat is mostly water and trace amount of salt. It dissolves easily in water.

> Water alone doesn’t do a very good job of removing bacteria or dirt

We agree here! (With some qualified reservations about what the subjective "very good" means, and how necessary it is for body washing applications.)

Water does a reasonable job of removing bacteria -- handwashing studies show this. It's a lot better than nothing. Yes, water combined with soap does a better job.

> If water alone did a good job of removing bacteria, then surgeons wouldn’t scrub with soap for 15 minutes.

The topic under discussion is body soaps, not handwashing.

I would always suggest washing your hands with soap! You use your hands to prepare food and touch mucus membranes. The same is not true of, say, your armpits.

(Going off into the weeds here, but: surgeons do not scrub for 15 minutes. That would destroy their skin and increase risk of transferring disease. Timed scrubs are 3-5 minutes. And they certainly do not perform surgery with their armpits.)

> Water does a reasonable job of removing bacteria -- handwashing studies show this.

If I'm not mistaken, the materials I've seen indicate it's the scrubbing for a certain period of time (20 seconds?) that removes the most bacteria in handwashing. Just putting your hands under running water alone doesn't do much, if anything.

Agreed — scrubbing is important. My comment about "water alone" was in contrast to "water plus body soap." I did not mean to suggest you should not scrub.

The goal of hand washing and body washing is the same: reduce the amount of remaining problem bacteria to a negligible amount.

Problem bacteria levels for hands and body are different. Hands are also typically washed for far shorter periods of time than showers.

Standing in a shower for 10 minutes doesn’t mean your armpits are getting cleaned well (or anything else for that matter). I bet most people scrub their armpits for a couple of seconds each. And except for people who shave, armpits are full of hair that interferes with getting them cleaned easily.

The set of people who vigorously scrub their clean-shaven armpits under water for 20-30 seconds each is probably pretty small.