Mark Kleiman has an insightful post that is definitely worth reading. Mark observes that even though Lott's work on concealed carry laws does not rely on his alleged survey, destroying his credibility means that people cannot trust the results of his concealed carry laws. Actually, there is actually no reason to trust the results of his research on concealed carry laws in any case, since it has been superseded by the work of Ayres and Donahue who repeated it using more data and better models:
"Those who were swayed by the statistical evidence previously offered by Lott and Mustard to believe the more guns, less crime hypothesis should now be more strongly inclined to accept the even stronger statistical evidence suggesting the crime-inducing effect of shall issue laws."
Ayres, I. & Donohue, J. 2002. "Shooting Down the More Guns, Less Crime Hypothesis" Stanford Law Review
Mark also suggests observes that permit holders very rarely commit crimes, so carry laws could not cause increases in firearms crime. However, carry laws could cause criminals to carry more frequently and increase crimes that way.