Dave Karpf of Rutgers University wrote a clarifying piece recently entitled, "Slacktivism as Optical Illusion", in which he describes how online Activities labeled (with a negative connotation) as Slacktivism can either be a waste of time or may actually serve a larger purpose.  It depends on how the activity is carried out.

He makes three points for explaining how slacktivist activities can be meaningful:  First, they should strategically be used to attract mainstream media attention.  It's pointed out that, today, journalists and editors actually turn to social media in order to pick out potential stories worth covering.  Second, they should have a specific target in mind.  For example, a general online petition to "stop animal cruelty" is guaranteed to make no difference, whereas the type expressing displeasure with specific corporations has a history of leading to successful policy change.  And third, organizations should develop relationships with people who've engaged in simple acts of digital engagement over time in order to "ladder" them up to larger-scale activism.

Great points all, and it's refreshing to read something of a how-to guide for constructive slacktivism rather than just yet another venting of frustration about it.

Something else that may be added to the conversation is how slacktivism is related to the decline of civic engagement in America more generally.   Robert Putnam described in his classic book, Bowling Alone: The Collapse and Revival of American Community, how social structures, or community-building organizations, from bowling leagues to weekly poker games to church-going Sundays, have been experiencing a major decline in participation for decades.  This decline in community-related activities has led to a decline in civic engagement and political participation as well, as more individuals engage in solitary activities disconnected from others.

Online social networking has raised the question since its inception of whether it fosters the concepts of "networking", community-building, and civic engagement, or whether it works against it.  And slacktivism is a strong component of this question.  If you tweet expressing support for a cause, does that make you more likely or less likely to engage in different forms of activism on the cause's behalf in the future?

Karpf is on the right track.  More ideas need to be generated in order to make "more likely" the more frequent answer.