TFA makes the point that, at least in theory, you can bandwidth-limit your router so that the amount of flow your neighbors generate is negligible. Someone who's driving through your neighborhood and is lost can pull over and look at a map on their handheld device, but the guy in the house next door won't be watching netflix all night on your connection and bogging you down. Another thing to realize is that if you have cable modem service, you're sharing bandwidth with your neighbors anyway.
For me, the big argument against doing this is simply complexity. Running a home wifi network for my wife and kids is already the biggest %*&%^*& pain in the ass ever. The damn system is fragile as hell. I've tried various things advised by slashdotters (buying brands and models of routers known to be reliable, using a surge protector and battery backup to avoid frying electronics), but the plain truth is that I've utterly failed to make a robust system and I experience constant hassles. It's like working on my own plumbing -- I acknowledge that I'm not competent to do anything more complicated than replacing a washer, and I don't want my plumbing to be a system so complex that it requires frequent maintenance. Others' mileage may vary, and many people here are certainly more competent than I am at networking. If so, more power to them. But personally, I don't want to stress my rickety system any more than I have to by having my neighbors on it.
A final issue is simply that wifi tends not to propagate very well. Even within my own house, I have trouble getting decent signal strength from downstairs to upstairs. I've installed repeaters and high-gain antennas, and it still doesn't work well. Our house isn't a mcmansion, but we have hardwood floors, and I think the building materials must really attenuate the signals.