We don’t all blog and tweet for the same reason, and I think that is okay.
I blog and tweet mostly for myself. I do these things to reflect upon my learning and to create a community of those who are interested in learning along with me. While I really like how you have framed the moral and urgent need for blogging and participating in social media, I wonder about the other reasons that folks do it besides “profiteering.”
Is it okay to blog as a way of simply capturing your learning? Is it okay to tweet simply because it is how you model connected teaching? Personal branding is not enough of a reason to create a space for yourself online, but I do think that teachers need a voice and one of the easiest way to cultivate one is through blogging. You should always know “why” you are engaging in some type of professional practice, and blogging is no different. But, I do think you can discover why you are doing it after you have been convinced to start engaging for less than admirable reasons (i.e., because someone advocating for the latest fad told you to do so).
I think many folks continue blogging for different reasons than they started blogging. I have had at least 5 different roles in education since I started blogging in 2004. It has shifted and changed so much during that time, but like you, I’d like to think that my persistence is about having a greater impact than I could otherwise.