I'm not sure that hard and fast "do not" statements are the most useful here.
For example, if a res square is 5 from another player, and if you know they aren't harvesting from it, then heading in and responsibly harvesting would seem entirely reasonable. However, if they are harvesting, the deliberately bumping would seem rude, camping on it would seem obnoxious, and harvesting to destruction would seem outright aggressive.
In the last couple of weeks I'm aware (as, for my sins, I have "Diplomat" in my alliance role) of around twenty instances of people harvesting within 5 or 10 of a city:
* In a couple of cases I only know because we got a "I'm harvesting here, but tell me if you'd rather I didn't email".
* In half the remaining cases, nobody much cared.
* In the cases where it was an issue, almost all cases were resolved by an email saying "err, you don't really have a claim to that - what are you planning?" - in these cases a quick discussion led to an amicable agreement (generally in favour of whoever is closer, but sometimes with more complex arrangements based on who is actually going to invest in gatherer units.)
* In one case, we sent the usual friendly email, and got in return a "rah! I will fight for that square, even tho it's miles from me!" reply.
* In one case, someone just sent in troops.
So, in summary...
I'm seeing lots of cases where harvesting is occurring close to towns, but generally people are being reasonable about it.
There is nothing in this new game feature that forces people to behave like jerks. If a minority do choose to be aggressive, then that's exactly what it is - their choice. It's not an inevitable function of the game.
The best way to deal with this, IMHO, is simply to continue to behave reasonably, rather than to expect any hard and fast rule to be adopted.
The question for "the community" may not be "what should the rule be?", but "what (if anything) do we do about the jerks?"