The whole idea of hacker news is to keep things simple. I enjoying spending time on this community. I find tags creating clutter. One person will tag "C" other "C programming" and someone else "Programming in C".
But it might be at least partially solvable by offering the user a choice between existing tags before allowing him to type in his own phrasing.
Or, once the user has typed in his own phrasing, a search could be done on existing tags and the user could be presented with a list of matching tags to pick from.