It's just another feature that people have been wanting since it was hinted at. Similar to any suggestion or hint (such as the Mod API) it has been vied for since their inception. But I can agree with the OP on this one. If dragons were added to the overworld there would need to be some serious balancing going on not just with the dragons themselves, but with the combat tools players are able to use. We don't want to see players farming them for XP or drops, nor do we want to see them riding them around destroying player's houses and builds.
I think that 1 dragon is enough.
If those red dragons were added in future updates
I can live with it, but it would be annoying.
And this is how i can imagine the scene:
Me: *takes a stroll outside of home* Oh, look a dragon *turns to the left*
Me: Oh, look another one
*<Player> was burnt to a crisp by Red Dragon*