The principle does apply, in philosophical discussions, but in the real world, things are look at quite differently in some particulars.
Freedom of speech, freedom of expression are things who's legal limits are interpreted by our courts, and while many things that once were taboo are now much more permissable, it seems the opposite holds sway with firearms.
Because so many people confuse a statement with an act.
Once upon a time, burning our flag was considered an act, and one rather frowned upon. Today it is considered an expression of free speech, and therefore protected from govt interference under the First Amendment.
An atristic display of firearms would clearly be an expression, but today it seems like the ordinary folks can only see ownership, or enthusiasm for firearms as "dangerous nut with a GUN!!!!!!!!" After all, that's what they are being told they should see, virtually 24/7 by our entertainment/news media.
I do believe that ownership of a firearm (any firearm) is as least as valid an expression of free speech as any dung smeared religious icon in a tax payer funded art exhibition. Probably a bit more so...
But the public perception of guns is not as art, but of brutal killing machines. Again, just what they are being told...
As arms enthusiasts, we see the art in design, and execution, not merely the result of use and misuse. People don't seem to have any problem understanding the appreciation of the style and engineering of automobiles, even if they don't have it themselves. Not so with guns, not for the majority, at any rate.
So eventhough you or I might see something as art, or an expression of free speech, many others see only a threat to their safety. And with the media "teaching" them in one way or another that this is what they should see, its not likely to change soon.