The difference between folk music and the whole rest is that folk music is ALIVE. Trying to 'protect' it by forbidding new things to be added is like sterilizing or even castrating it. Forbidding it to breed is like killing it. Hehe - trying to kill it - you won't succeed.
What we call folk music is the music that has survived, while 'non-folk' music has died. Of course the surviving (=folk) music isn't new, it takes some time to wait until all concurrents are dead.
So I think it's wrong to consider a new (recently written) song to be folk or not. Just wait 50 years and then see what's happened to it. Will it still be a 'piece of music' which must be performed some special 'correct' boring way or will it have grown to a real 'song' being performed in thousands of different versions where each of them is new and interesting? THAT's folk.
And the only thing that needs protection is having the guts to perform a song you like YOUR! OWN! way.