I think we've discussed this in various ways, in different places, but maybe it deserves its own thread?
Below I've quoted/adapted some statements about Sherlock: Premise #1. Sherlock is transforming into a better person throughout the series due to John's influence.
Premise #2. Sherlock is already a better person than anyone (including himself) thinks he is, but it is being revealed through his relationship with John.
Premise #3. Sherlock is not a good man and never will be, with or without John.
Premise #4. "Good and bad" are concepts that do not apply to Sherlock.
Take it in any direction you like, and discuss!