I have to agree. If it was about tradition, would we have ballroom dancing and not cross country? For a more recent example in the world of running/T&F, should the women's steeplechase not be a part of the Olympics because, just a short time ago, it wasn't? Women's pole vault?
As for the argument that it should be really hard to get in, is one more event going to suddenly make it easy? Three more American (just to pick a country) men and three more American women, assuming nobody who is running the 10,000 doubles back in the half, will get in.
Personally, I'm intrigued by the idea of an Olympic half marathon. It's an amazing race distance and you could have some epic competitions at that distance. On a related note, I've for some time been in the camp supporting a return of cross country to the Olympics.