What is unpersuasive about the responses to Mother Jones?
I agree that Duwe's point is the closest thing there to a decent argument against MJ's data. But I think the accusation that there data is "cherrypicked" is not reasonably supported. The entire paragraph in Siegel's piece where he argues for this is essentially ignoring that what they are using is what fits closely with the common intuition of what is a mass shooting. The only one which one could plausibly take out of that set is Fort Hood but it doesn't alter the data very much.
Most of Siegel's points are correct but not relevant to the question of increases of shootings. For example, he's correct that there's a serious measuring issue with whether shootings are stopped by others with weapons, and he's also correct that even if the trend identified by MJ is accurate it is still a tiny fraction of total crimes and will remain so, but that's not actually relevant to evaluating the central claim.
What about the methodology of starting with news reports? These have strong biases that probably change by time. And how did they locate decades old news reports? A recency bias is to be expected. (Added: Duwe has a paper about this!)
Their definition is pretty reasonable, except for the part where they make tons of exceptions. The examples they gave of the exceptions that they made sound intuitive, but what about all the exceptions that they didn't talk about? Why didn't they include the Ridgewood Postal murders? Since they don't actually have a consistent...
What is something you used to believe, preferably something concrete with direct or implied predictions, that you now know was dead wrong. Was your belief rational given what you knew and could know back then, or was it irrational, and why?
Edit: I feel like some of these are getting a bit glib and political. Please try to explain what false assumptions or biases were underlying your beliefs - be introspective - this is LW after all.