A tag of "ABCD" should be treated the same as "abcd" ["aBcD" or any other combination] in tag database. It is absurd to differentiate between cases, the tags are not very precise semantic data and applying a programmers convention to community data is backward and lazy. One method / function is all it takes to clean up the mess.

Furthermore, when making a search, all input should be converted to whatever case the database is stored in so again, "ABC" matches "Abc" which matches "abC" etc.