Earlier quoted context omitted.
It was posted elsewhere that the gun, while legal to manufacture and possess, is illegal to transfer to another person in any way. Given that, destroying it is perfectly reasonable if he didn't feel like owning a homemade AK-47 forever.
That's a good point, but it's not completely true as stated. It is illegal to manufacture a firearm for sale or transfer without an FFL (a Federal license). However if I'm reading this[0] right it is probably not illegal to manufacture a firearm for personal use, and later sell or transfer it to another individual. It would need to be a legal sale under CA law, meaning I guess it would need to be serialized and regis…
Book burning used to be seriously reprehensible, because it was a potentially effective way to destroy or deny information. If you were burning Bibles in the 14th century or whatever, you were making it vastly harder for locals to find out what was in a Bible. A successful book-burning program could seriously alter the information available.
Today, though, book-burning is pointless except in some rare cases. It's definitely pointless to burn Bibles or anything else that exists in multiple copies. Yet we still find it to be reprehensible. Why?
I think part of it is just history. We remember that it used to be really awful, and we're slow to catch up.
But part of it is the symbolism. We know that it's not really destroying information or impacting anyone's access to it. But that's still the intent. By burning books, you're declaring that you want to deny people this information, even if you can't. Well, sometimes you are. Other times you're just disposing of paper and ink to no ill effect. It can be hard to tell them apart.
I think the AK-47 here is much like burning a widely available book. There are tons of AK-47s out there, so destroying one won't impact its availability in any meaningful way. It ultimately does nothing to destroy one. On the other hand, it may be symbolic, saying that you want to deny people to these guns, even if you can't. Or maybe it's just pragmatic. Hard to tell exactly which one applies here.