The problem with Gladwell is he will be read by literally millions of politicians, school administrators and middle management drones. They will read it as science, and because they do not understand science, they will use the easy approximation of science=truth (especially if they can fit it into their worldview (which Gladwell is extremely good at assembling an argument to do)). From the propositions "Gladwell uses science" and "science=truth", they will not "spark conversation" but instead will progress to "Gladwell=truth".
This leads to two bad things:
1. People start spouting crap Gladwell has said at parties because it is "scientifically proven" as if it were the unvarnished truth.
2. Your boss will start new initiatives to find the customer "tipping point," hand out "maven" badges to favoured employees, or think because they have been doing something for years, Blink shows they don't need to learn anything new, listen to others or do any analysis.
These things are negative externalities. I'm not sure you could value them, but it is at least conceivable some CEO of a large company will make a stupid decision based on something he read in a Gladwell book. (Okay, maybe I should lighten up...)
I guess what pisses me off is he is using our work as scientists to generate a large profit for himself at the expense of both the public's understanding of science and the careful use of science in policymaking (e.g. supporting broken windows v.s. abortion as the reason for the '90s drop in crime.)