I see it this way. Most of the time, those coins aren't going to be slabbed. In fact, most of the time, those coins are going to end up in that person's PERSONAL collection. Which means, if they want to scratch them, hold them, gargle them in their mouth or whatever... it's still their coin!
I also see that "most" of the time folks aren't expecting the coin to be a rare coin..> They're just looking for the date or trying to figure out what it is. I rub coins all the time. Why? I've NEVER found a single silver coin, or coin of value. After having rubbed 1000+ coins clean of the dirt to figure out what it is, if I'm wearing a go-pro for my own enjoyment, the likelihood that I'm then going to magically start using water is unlikely. In fact, I'll probably rub it, thinking "just another copper" then get completely excited, then bum myself out that I rubbed it, then go back to being excited... AFTER the fact. And then that 1877 penny, 1914-d, penny, or 1955 Double Die penny is going to go into MY collection. In the end, I'll get just as much enjoyment out of a penny that has scratch marks, than if the penny didn't have scratch marks. Functionally, it only has less "value" to someone who cares about the scratches.
As a prime example, I LOVE holed coins. Why? Not because of the hole, but because I get all the fantastic "Extra Fine" details of a nearly new coin, at a bare fraction of the price of one without a silly little hole. I don't care if it has a scratch on it, or a hole in it, I'm there to enjoy the beauty of the details, and the history I hold in my hand. I'm not in it for the investment, or the sales. If I can get a coin without a hole, great! But some of the coins are so far out of my price range, the only way I can enjoy that history is finding one that others think is "wrong." Wrong for them is right for me! LOL
That's the way I see it. Crud... my first Walking Liberty half, I ever bought, I promptly went home and scrubbed it with baking soda, just to see what it would have looked like "new." I KNEW it was destroying the re-sale value... but I found MORE value in the learning process than the $1 I lost in coin value. I love that coin... look at it frequently, and have enjoyed it thoroughly... even though it's worth bullion at this point, probably. In fact, of the 4 Walkers that I have, its still my favorite. The others may be more "natural" or "detailed" and definitely have been cared for from a history standpoint...but that cleaned coin is still my favorite. I can't explain it, other than to say this:
The reason I love the coins is not because of their value to someone
else, but rather because of my enjoyment of the coin.
Some folks may look at it differently. In fact, I know collectors who pride themselves in having the priciest coin on the block (or most expensive equipment, or nicest car...etc.). That's where they get their enjoyment. In fact, I may love the 1877 crusty dirt-rubbed-scratched coin MORE than a "better grade" I'd bought at auction. It may be the experience that makes it enjoyable... who knows.
In economic terms, this is called "maximizing your utility." Some folks maximize the value of the experience by checking RIGHT THEN, the date... others maximize the experience by the anticipation of the find later in the water. To each their own... heck... we all enjoy our hobby slightly differently (different equipment, locations, styles of searching, with a buddy, without a buddy, in a club, alone... etc.)
It bothers me a bit (not a lot... just a bit.

) when people wonder/believe/accuse that someone may be enjoying their hobby "wrong" because it's not the same way they enjoy it.
If someone buys a classic car with the purpose of putting it in a garage to look at it, and to enjoy "owning it," does that make it not ok for someone else to buy a classic to drive it? In the same way... rubbing a coin is driving the car (putting wear and tear on it). Just like driving a classic car lowers the value through wear and tear, some owners are in it for the experience of "handling" the car. Coins are like that. Digging is like that. Some of us are into the hobby for the experience, not the resale value.
I love how we all enjoy our hobbies differently. It's what makes talking with others so much fun.

When I see someone rub their coin, it doesn't bother me... it's their coin! If they get wet-pants excited over rubbing the dirt off to see the date, then go ballistic in enjoyment... I say we should all let them enjoy it! It's highly unlikely we'll ever buy it anyway... and if we do, we'll get it cheaper. LOL
Skippy