Granted. I worded it poorly by saying "indicated". I meant basically the same thing as you're saying. His argument is pretty silly...saying that there is no evidence of something so it's probably true is pretty illogical. I just meant that the lack of evidence COULD just as easily be because it doesn't exist...or as you said "We know nothing about Q if P is false".
Edit: Stat, you're right, there are plenty of incidents of accidental discharge in the home, fatal, injury, non-injury, whatever the case may be. I have definitely read a few about accidents due to CCW, if you read JLee's link from the NRA (the blog with news articles about CCW related incidents) then you'll find a few of them. I think one was even on the first page. The question is, why haven't they been compiled into a cohesive counter-argument? We can't know that. Sure, maybe it's because "it's obvious" as you say, but since when has that ever been a common argument on important social issues? I think it's more LIKELY (although again, there is no way to know) that there is little to no compilation or statistics for these incidents because they are so few as to be worthless...or at least worthless to the counter-argument.