Voldemort's humiliation of Bellatrix in The Dark Lord Ascending makes me very sad, but some people (especially Bellamort deniers) blow it out of proportion. It was very mild compared to how he treated everyone else. Even in this scene, the Malfoys were treated far worse. This is the worst thing we ever see him doing to Bellatrix and I would take this over his murder of Snape and his treatment of the Malfoys any day.
“Why do the Malfoys look so unhappy with their lot? Is my return, my rise to power, not the very thing they professed to desire for so many years?”
“Of course, my Lord,” said Lucius Malfoy. His hand shook as he wiped sweat from his upper lip. “We did desire it — we do.”
To Malfoy’s left, his wife made an odd, stiff nod, her eyes averted from Voldemort and the snake. To his right, his son, Draco, who had been gazing up at the inert body overhead, glanced quickly at Voldemort and away again, terrified to make eye contact.
Voldemort targets Bellatrix only after she defends the Malfoys. She had no reason to do so and it's highly unlikely he would have targeted her if she hadn't said anything.
“My Lord,” said a dark woman halfway down the table, her voice constricted with emotion, “it is an honour to have you here, in our family’s house. There can be no higher pleasure.”
What's most interesting here is that Bellatrix calls Malfoy Manor ‘our family's house’ even though she's not a Malfoy but a Black who married a Lestrange. Malfoy Manor isn't Bellatrix's family home, but by calling it that, she's positioning herself with the Malfoys, counting herself among them in their moment of disgrace, and that's exactly what Voldemort doesn't want. He's punishing the Malfoys by taking over their manor and humiliating them in their own home, and instead of standing apart or staying silent, Bellatrix attempts to protects them from him, trying to deflect his attention from their obvious terror by showing the enthusiasm they can't muster.
“No higher pleasure,” repeated Voldemort, his head tilted a little to one side as he considered Bellatrix. “That means a great deal, Bellatrix, from you.”
Her face flooded with colour; her eyes welled with tears of delight.
“My Lord knows I speak nothing but the truth!”
Even though she also spoke for the Malfoys, he singled her out and made it clear that it meant a great deal only from her and not from them. He makes sure to be as obvious as possible that it's only her opinion he values and not of the family she's defending. He knows the Malfoys don't share it but since she grouped herself with the Malfoys, Voldemort treats her like one.
"No higher pleasure … even compared with the happy event that, I hear, has taken place in your family this week?”
Notice what he actually asks, though. He forces a direct comparison between himself and her family by asking this. He's making her prove that he matters more than family. It's his pathological insecurity and his fear of abandonment that are driving this. A secure person wouldn't need to rank themselves against family, even sarcastically, but Voldemort cannot tolerate being second to anything. He weaponises her 'no higher pleasure' declaration by making her prove it against family, exposing his desperate need for absolute priority over every other bond in her life.
And he does this only to her. He mocks the others about the marriage, but it’s only Bellatrix he asks if he means more to her than her family. Her devotion matters to him in ways the others' don't, which means her family loyalties pose a personal threat that requires neutralisation because he's triggered by her solidarity with the Malfoys.
Family loyalty, for her, is the one bond that could rival his bond with her.
She stared at him, her lips parted, evidently confused. “I don’t know what you mean, my Lord.”
“I’m talking about your niece, Bellatrix. And yours, Lucius and Narcissa. She has just married the werewolf, Remus Lupin. You must be so proud.”
Bringing up Andromeda and her daughter also conveys his disapproval of her defence of her family, as they're technically still her family even though she had distanced herself from them. More than disapproval, it's a trap. He's essentially reminding her of the other family. If family is who she is siding with over him, he will examine all her family and ask her if they're worth it.
“She is no niece of ours, my Lord,” she cried over the outpouring of mirth. “We — Narcissa and I — have never set eyes on our sister since she married the Mudblood. This brat has nothing to do with either of us, nor any beast she marries.”
This confirms she was protecting her sister throughout, but that protection was precisely what triggered something volatile in him. This entire exchange reveals his need for her specific validation, then immediately tests whether that devotion is absolute or not. He responds to her defence of Narcissa by targeting the person who means most to Cissy, Draco:
“What say you, Draco?” asked Voldemort, and though his voice was quiet, it carried clearly through the catcalls and jeers. “Will you babysit the cubs?”
The hilarity mounted; Draco Malfoy looked in terror at his father, who was staring down into his own lap, then caught his mother’s eye. She shook her head almost imperceptibly, then resumed her own deadpan stare at the opposite wall.
The ending reveals what this was really about. Voldemort stops the laughter when Bellatrix is about to cry. Then he immediately offers redemption through the 'pruning' mission.
“Enough,” said Voldemort, stroking the angry snake. “Enough.”
And the laughter died at once.
“Many of our oldest family trees become a little diseased over time,” he said as Bellatrix gazed at him, breathless and imploring. “You must prune yours, must you not, to keep it healthy? Cut away those parts that threaten the health of the rest.”
"Yes, my Lord,” whispered Bellatrix, and her eyes swam with tears of gratitude again. “At the first chance!”
“You shall have it,” said Voldemort. “And in your family, so in the world … we shall cut away the canker that infects us until only those of the true blood remain.…”
The redemption is exclusively hers and not Lucius or Narcissa's despite Tonks being their niece too, or Draco's who was mockingly asked if he'd 'babysit the cubs.' The humiliation was collective, for all of them were mocked over Tonks's marriage, but only Bellatrix received the kill mission. Voldemort isolated her for this task because he only wants her bound to him through familicide. Only she gets elevated from victim to executioner, and she did pursue Tonks obsessively afterwards.
Notice also the pronoun shift. He's realigning her identity from 'Bellatrix defending her family' to 'Bellatrix and Voldemort against her family.' The 'we' reinforces their bond that excludes everyone else and frames her no longer the patient whose diseased family tree needs treatment but the surgeon alongside him. The humiliation was preparation for this adoption. Now she belongs to him, not to them.
The 'pruning' metaphor becomes even more interesting when you remember Voldemort's own history. He murdered the Riddles and cut away that canker from his own family tree, and now he's asking Bellatrix to replicate his familicide. He's making her into exactly what he is: a family murderer. The intimacy of their 'we' makes even more sense in this context. They'll both have crossed that line together.
It's highly likely it was he who tasked her with killing Sirius Black. When Voldemort arrived at the Ministry to find the prophecy destroyed, Bellatrix's immediate defence was revealing that she'd killed Sirius. She thought killing Sirius would mitigate the prophecy loss, and the nickname they had for him, the Animagus Black, implied prior discussions of him. He was another Black family blood traitor for Bellatrix to prune and Voldemort weaponises her against her own bloodline, binding her to him through the murder of family members. Each kill severs another tie that might compete with her devotion to him.
Here, he was not just likening the Tonkses to canker but also the Malfoys. Even though they're Pureblood, they're disgraced and teetering dangerously close to blood traitors, and he wanted her to stop defending them.
Her family loyalty threatens him, so he lashes out and her devotion feeds him, so he protects her. When she wavers toward family, he reclaims her. The obsessive devotion he cultivates in her happens because he unconsciously needs it. He fuels her obsession with him deliberately and it all stems from his abandonment trauma.
I wonder, if in time, he would have asked her to kill the Malfoys too.