It's not like they havent been invaded already...
Conscription is always controversial and the questions of national identity that have in the past provided a social framework for supporting it are much fuzzier now. The question of "What is a Swede" would no longer be a theoretical one. On the other hand, almost all extant nationalities were hammered out on an anvil of blood soaked fields...
I believe there is some racism as there is everywhere, but overall I think the armed forces are a place where someone who came as a refugee in on more even terms with others than anywhere else before that.
Source: http://www.statistikdatabasen.scb.se/pxweb/sv/ssd/START__BE_... (official gov't statistics)
So +200 years without war and counting
The world has been at war several times and Sweden has fought only a few times on small scales. When you building is on fire, but your are safe in your flat, it's not a moral decision to lock your door and goto sleep for the night.
Well, many others were also warring a lot then, but the change was quite abrupt in Sweden, and then the country even managed to stay out of WWI and WWII.
Of course, in Cold War it was actually operating with the U.S. but the war was not, well, hot.
You can either view it as Sweden being ruled by Denmark, or a EU style union between equals, in which case 1523 is more of a Brexit situation.
There are decent arguments on both side. I lean towards the latter view.
Instituting a National Day in to remember it is more a modern way to try to keep up with the neighbors. All other countries have a national day, so we should get one too, even though we're not really sure what to do with it :)