.... Oh, Peter! - sounds to me like you're on the verge of the "caving certificate debate" and we all know what happens when people wander down that jagged route.
Of course it's good when people are proficient in anything rather than engaged in Do Yourself In techniques.
Dep: the person organising the trip is supposed to ensure that people have the correct equipment, surely? It's up to the leader to tell people what to bring and if they don't personally own kit you can either hire or borrow it on their behalf.
Whitelackington: you mention beginners on ladders. Where should people be getting their first ladder experience? (on the surface is the correct answer). Of all people, which are most likely to make a mess of climbing a ladder? (beginners is the correct answer). Therefore is it such an unreasonable thing to suggest that the people most in need of a harness should be the ones who ought to wear one?
If you wish to take the harnesses off and stow them in a bag downstream away from the pitch/waterfall (where it is cold and unwise to stand around waiting BTW) then that's fine but I've often seen cavers (and done this myself) wearing a harness to Sump 1 and return again.
The people who own the kit are the people who look after/maintain it.
Caving is expensive already but then as we all know, cavers are so tight they can manufacture their own diamonds by sticking lumps of coal up their backsides. When you buy a car do you complain about the additional cost of the seatbelt?
Ladders snap, Dep, and an awkward fall of 2m/6ft onto rock(s) can be fatal.
Oh, and remember:
"The single biggest cause of death/injury in UK caving is (was) falling unlined while climbing ladder pitches of 10m or less": this statement may have since been superceded as a result of better training, better equipment and people undertaking more suitable trips within their capacity.