That's because such a thing doesn't exist. Any snippet from a Tesla website used as supporting evidence that 'local supercharging is unethical' is just someone's creative interpretation, very much biased towards how they want to view the situation.
What is really comes down to is that nobody wants to wait at a supercharger for a stall, especially if they're waiting for someone that's just trying to save $3.85 in electricity that night...and who could blame anyone for getting peeved at that kind of situation? The moral of the story is and has always been to use a little bit of common courtesy when charging locally...even if you're the only one extending that courtesy.
I was trying to avoid this thread, but I can't help but put it out there. Ethics does not need a sign or explicit ban. For example restaurants will not have a sign that says: don't take more napkins or sauce packets than necessary, especially if you are using it for home. However, even in the absence of such a sign, I'm pretty sure a lot of people will feel someone who shoves a stack of "free" napkins into their bag for use at home is being unethical (although the person doing it usually doesn't, because they "paid" for it with their meal).
And looking at the Tesla's text on this, it's blatantly obvious the primary use case is roadtrips/long distance travel.
minimize stops during long distance travel
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have enough range to get to your destination or the next station
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We strategically place Superchargers along well-traveled highways
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http://www.teslamotors.com/supercharger
How does Tesla decide where to put the Superchargers?
Tesla places Superchargers along the most popular road trip routes, accounting for distance and local driving conditions.
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What is a Supercharger and why is it unique?
enabling convenient long distance travel in Model S.
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Why is it free?
We want to encourage Model S owners to take road trips.
http://www.teslamotors.com/support/supercharging
Tesla Superchargers enable free long distance electric driving
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Model S drivers enjoy the convenience of plugging in at home or at the office so they’ve always got plenty of charge for their daily driving needs. Tesla’s global Supercharger network makes road trips exceptionally easy and delightful.
http://www.teslamotors.com/blog/2000-superchargers
I'm not seeing how anyone can say with a straight face that Tesla does not primarily intend the supercharger to be used for roadtrips and long distance travel given how much it references such usage. And all of the marketing done so far for superchargers (recording breaking trips across country) demonstrate long distance travel, not local travel. In fact the last blog entry suggests that drivers use home/office charging for daily driving and supercharger network for roadtrips.
The only suggestion I can find in all that material that is even close to what the OP is suggesting is this part:
We strategically place Superchargers along well-traveled highways and in congested city centers.
http://www.teslamotorsclub.com/show...of-a-Model-S?p=1027218&viewfull=1#post1027218
I touched on this on another comment, but previously it said this:
We strategically place Superchargers along well-traveled highways and in congested city centers where home charging is difficult.
https://web.archive.org/web/20150113072623/http://www.teslamotors.com/supercharger
That "home charging is difficult" reference was removed in the same time frame where Elon was getting a lot of flack for low sales in China (one of the countries where superchargers are installed in congested city centers) and he blamed sales people there for overemphasizing the difficulty of charging in China.
http://www.businessinsider.com/elon...-have-been-blown-way-out-of-proportion-2015-2
And the city superchargers (multiple per city) were added to address cities where people live in apartments without home charging (I can dig up the references if necessary, most of it are mentioned in presentations with shareholders/customers).
I do agree someone that moves their car is obviously much better than someone who doesn't. But why people would think it is even little bit unethical (and not have the same thoughts for someone using for roadtrips) I think largely has to do with how Tesla markets the superchargers.