well, insofar as the internet is a very good mobilizing tool for white upperclass men in the global north, organizing those communities online, even exclusively, might make a lot of sense.

but if the community organizing has any interest in diverse communities or subaltern communities, the internet will only be a tool that leads to real-world action -- a tool that is not accessible (because of economic, language or educational barriers) to everyone.

even leaving that aside, though, i'd say just on a philosophical basis that you actually have to be present within a community before you can hope to organize it; that ultimately the goal should be for self-organization. the road to hell is paved with good-intentioned humanitarians eager to "save" a community from itself. most of the sociological studies of social movements in the last half-century, from saul alinsky to paolo freire to starhawk and the zapatistas, have emphasized being fully present and part of a community before one does any sort of "organizing." (other people, like frances fox piven, would say that people can only effect change within the groups of which they are a part, because the most effective knowledge is a kind of foucauldian communal self-knowledge...but that is a discussion for another day...)