Good literature rarely offers simplistic moral lessons. Instead, Richard III by William Shakespeare is a historical drama that vividly portrays the War of the Roses and gives an audience a complex and subtle analysis of character to help understand how the personalities involved may have shaped historical events.
The villain of the play is, of course, Richard III himself. He is responsible for multiple murders of adults and children, including his own relatives and anyone who stands in the way of his ambition. As with many of Shakespeare's villains, he can be charming and articulate, although lacking remorse. It might be possible to read into this lessons about the limitations of monarchy as a system, following Lord Acton's dictum that power corrupts and absolute power corrupts absolutely. It is unlikely, however, that Shakespeare intended that as a lesson to take away from the play. The hero is Henry Tudor and the play thus flatters the Tudor dynasty and in fact celebrates the just monarch just as much as it condemns the unjust one. One can though legitimately draw the conclusion from this, as from Macbeth, that ambition untrammeled by morals or responsibility will overreach and lead to dramatic downfall.
Another important issue is Richard's disability. Much of his character was formed by a life of constant pain and by the discrimination of the able-bodied against him, something that has made him embittered. Perhaps a lesson to be drawn from this is what is now known as the cyclical nature of abuse, where the abused become abusers and the bullied become bullies.