You know what's fukk up about Rhaegar is, his silly delusions aside (though he was fighting for the greater good, he completely overlooked that his decisions would get his ass killed, his wife/kids killed and his family slaughtered), he probably would have been a great king. Exactly what the realm needed after Aerys.
Basically three things got everybody murked Robert not knowing Lyanna didnt want his azz, Rhaegar marrying a chick he didn't love and Barristan not letting that crazy fukk die in Duskendale. If Rhaegar didn't marry a Martell, he'd been free to marry Lyanna. Robert would want to start a war but, without Aerys there burning muthafukkas, tempers would cool and Rickard would be because his daughter would be the Queen of Westeros. Robert would just go back to the Stormlands and sire 20 b*stards with various whores. Everybody lives. Ned and Ashara get to be happy ever after and Brandon has to go back to Winterfell and put up with Catelyn until he dies
It's because Rhaegar was a fukking puzzy. That's all.