I agree to the extent that you shouldn't lock a firearm in your car if in a crime-laden area or it will be unattended for extended periods of time like an airport or train station, but that aside it's a viable, practical and sometimes necessary option - been doing it for 30+ years and never had a problem. Heck, cop cars have them locked in plain view - in fact, our motorcycles had M-4s mounted and locked externally - cops aren't in the habit of brining their long guns into the donut shops.

Ultimately, I want to keep my weapon on my person, that's what I have it for, but sometimes...
I am confident that at one time or another, the vast majority of members on this site have locked firearms in their vehicles without incident, especially long guns.