Derik Badman has a new article up over at Comixtalk about the general trend of defining "comics" and "why we should stop bothering." This is similar in nature to an academic article by Aaron Meskin that I've continually not gotten around to reviewing here for the last several months.
A few concerns: In general, the task of defining "comics" is like any other quest to understand how categories and conceptualization works. And, as Derik points out with a reference to Wittgenstein, it is very difficult to exact any rigid definition with regards to anything.
This is one of the reasons my forays into this discussion usually are UN-defining "comics" — because it's an attempt to deconstruct the notion past any rigid definition. Though I may be regarded as a culprit of the "definitions" club, the result of my attempts usually end up with a very vague and non-explicit definition that says "comics" means a complex of socio-cultural things including an object, industry, genre, culture, etc. (but not a medium).
That said, definitions and categories do matter, as can be seen in very realistic terms in debates over whether gays really can get "married", or whether water-boarding is or isn't "torture." In terms of this debate, we see it in other places like whether "graphic novel" has its own meaning or if it's an upscale synonym of "comics." In all these scenarios the result of the decided-upon definition has legitimate real-world consequences.
Like it or not, McCloud did set a definition in many people's minds for what "comics" means. These people often argue passionately in their absolute certainty that the word means exactly what McCloud said it does. Engaging in this discussion is to say: 1) McCloud may be wrong, 2) why?, and 3) what does that mean for how the word (and its referent) is used/treated in society?
Personally, I think that the most important fall out of such a discussion is to recognize that "comics" and "sequential images" are two entirely separate things (contra McCloud), and that such a separation yields extraordinary consequences. Those results end up seeing many of the branches on Derik's family tree of comics not as "comics" at all — with ultimately the notion of "comics" dissolving and marginalized to something else far more fundamental.