I'm not sure how making your wireless network open is the "socially responsible" thing to do anymore then letting strangers come in and use your bathroom at will is.
Sure, most people won't cause any harm, but it only takes one asshole (or too many people taking advantage) to make it a nightmare for you.
FWIW, I believe the idea is to segment the network so you are sharing your bandwidth, but not your "home network."
A closer analogy would be letting strangers use the outhouse on your property, but not letting them in the house.
The router used by Numericable here in France offers a "guest WiFi" connection out of the box. It is not enabled by default, mind you, but it is available nonetheless.
Probably the closest analogy would be seeding on bittorrent. No harm to you, beyond perhaps reduced network speed, but significant benefit to everyone else.
Unfortunately, in many countries[1] you'll be prosecuted as an accessory if someone commits a crime via your connection, unless you set it up in such a way that you're legally an ISP. This is obviously a lot of trouble, so you're better off not bothering.
[1] there have been a number of cases in Germany, for example
Do you mean "guest wifi" meaning one need not enter a WEP key, or do you mean "open wifi" like is being discussed here?
Because it is my understanding from reading the EFF page that they want the Starbucks model (open network and gratis connectivity), which differs from my experience with SFR/Orange/Neuf etc which are revenue-sharing deals [in my experience].
Even Netgear(? or perhaps D-link) in the US shipped access points with some kind of silly revenue-sharing situation.
Sure, most people won't cause any harm, but it only takes one asshole (or too many people taking advantage) to make it a nightmare for you.