I don't think they can do it alone. My basic difference with Doug is that he thinks you can pressure people with something negative to get them to stop doing something undesireable; I think you have to sweeten the deal to encourage them in a positive way to do something other than the thing you find objectionable.
[WS:] One needs both. If people were to change their behavior simply to respond to a better alternative without any regard to the cost/benefit to what they already have, we would have socialism in the US :).
The prescription for social change is to pull people by lowering the cost of the alternative and at the same time push them by increasing the cost of the status quo. You need both. One or the other simply will not do.
Wojtek