Look at the alignment line in the Black Dragon entry in the Monster Manual:
Alignment: Always chaotic evil
If it said, "
Usually chaotic evil", I might be more open to the suggestion that the black dragon's alignment was more a function of "nurture", rather than "nature". If a race's alignment entry says "Usually (blank) evil", it suggests that they're evil, at least in part, because they're raised that way...and, therefore, if raised to be "not evil", maybe it'd stick.
For example, ogres are "Usually chaotic evil". If a kindly farmer found an ogre baby, and raised it in a loving, "good" enviromnent, it's entirely possible that you'd wind up with a good-aligned ogre as an adult (and, in fact, "the misunderstood, good-aligned member of a normally evil race" is a story element that's been used many, many times in D&D adventures).
However, dragons (at least the 10 "true dragons" in the MM) are
always of a particular alignment (wrt law/chaos as well as good/evil). This suggests that there's something hardwired into the species that makes them that particular alignment, and thus, trying to raise them to be of a different alignment should be futile.