Poor Breezepelt. I mean, it was not his fault he ended up in the dark forest. It was Nightcloud, still spiteful about Leafpool, who made Breezepelt hate Crowfeather. And (CENSORED) Crowfeather ignored Breezepelt, thereby fueling Breezepelt's hatred for him! And when it was revealed that Crowfeather had kits outside Windclan, that would have been the final straw. Imagine if your dad neglected you all the time, your mother trained you into hating him, and you learn that your dad has three more kids with some other woman who was not supposed to have kits in the first place! Breezepelt had at first followed the warrior code, but he lost faith in it because his father Crowfeather and ex stepmother Leafpool destroyed it! He would have felt isolated and alone, and when Tigerstar offered him the chance of vengeance wouldn't you take it? The comment below the one directly below this is incorrect in the sense that Bluestar's situation was not as bad. She may have been neglected, but her parents were not that bad. And she was not approached by the dark forest, thereby she did not have the oppertunity to join them. If her parents had been like Breezepelt's she would probably be running to the dark forest by now. And Tigerstar had manipulated Breezepelt, playing him like a puppet on a string after learning how he might be persuaded to join. It was not Breezepelt's fault! In my opinion it should be Crowfeather who rots in the dark forest.
To anyone who just sees Mapleshade as another villain, to anyone who gets that grin when they hear that her soul was destroyed by Spottedleaf in The Last Hope, I wouldn't call Mapleshade a villain. I mean, she lost her mate and kits, and was banished to the dark forest, while 'unfairly' Greystripe will head off to starclan, his son Stormfur will survive, his mate Silverstream is waiting for him in StarClan, he has another mate, and more kits, and so on. Same with Bluestar and Dovewing, as well as, to an extent, Leafpool and Crowfeather (though for a duration their own children did not know about their parentage, and hated them for a few days when they learned it as they realized they were half-clan, as well as the children of a medicine cat, before they accepted their parents). Mapleshade was forced to watch as several cats got what she had been denied, along with a pleasant afterlife to boot!
Look at his childhood. He was physically and mentally scarred by an attack by Tigerclaw, was abused at home, and was hated by his siblings. Not much more to say here really.
He may have had ambition as a kit, but it was Thistleclaw who mentored him and who turned that ambition into cruelty. Thistleclaw was the one who goaded him to attack Scourge, was the one who trained him to love combat, was the one who trained him to get what he wanted, no matter how many people he had to kill. I don't think he deserved the dark forest really. If stupid Sunstar had chosen someone who would turn that ambition into loyalty then this would not have happened.