> Much safer to just gather information and give it to the police.
The police won't help you recover your stolen property: it's not their job.
> Confronting a thief in person is pretty dangerous...there's a non-zero chance of a fight, possibly involving a knife or gun.
Every day walking around a city involves a non-zero chance of a fight. Every day interacting with other humans in civilization can involve a knife or a gun. Meeting someone who opportunistically boosted your DSLR at a house party isn't significantly more dangerous than meeting any Craigslist seller in any public place. In fact, it's probably less dangerous, because you won't be walking up to someone you don't know with hundreds of cash dollars in your pocket.
It's not even a complicated meeting. You take a friend, for safety, as many craigslist buyers do. You ask to see the camera, as any craigslist buyer would. You ask to take a few sample pictures to make sure it works, as any Craigslist buyer would. You snap a picture of the perpetrator and tell him (politely, because you don't want to fight) that this is your camera and you're going to keep it; if he disagrees, he's welcome to accompany you to the police station to sort things out. The vast majority of opportunistic thieves at this point will completely bug out since they know they're busted and they don't want to go to jail (there are few DSLR/lens combinations that don't qualify as felony larceny in most states).
I find your vision of a world in which opportunistic thieves pack heat and victims "just gather information and give it to the police" unrealistic, not to mention depressing.