What you fail to appreciate is that the original tales and their variants are as much a reflection of the culture around them as Greek Myths are of Ancient Greece, and in comparison the twee, sweetened Disney versions seem like terrible perversions.
Consider the Little Mermaid. It has within it strong themes related to maturity and the female puberty, as well as a central argument: the juxtaposition of one's own selfish desires against a purer morality. Rather than kill the Prince for herself, the Mermaid chooses to let him be happy, and for that sacrifice is carried up to heaven; to that extent, the villain of the story is not the Sea-Witch, who is a simple means to an end, but the Mermaid herself, forced to choose between happiness or a greater good - in this case, compassionate love. Juxtapose this against the syrupy simplistic black-and-white morals of Disney's adaptation, and you see that it actually encuorages selfish behaviour and rejection of one's own culture and roots!