The atmosphere in the room had shifted. There was no specific reason for it that Steve could have pointed to, no change in Natasha's posture or facial expression, but it nonetheless suddenly felt as if the air was full of tension. Like the quiet stillness that settled over an area in the minutes before a storm struck. It was enough to set Steve on edge, bracing for something terrible, and as soon as Natasha began to speak, he could tell that whatever she said next was going to be her particular brand of vicious.
Natasha was perfectly steady, calm and quiet, and as soon as she brought Erskine's name into it, Steve flinched. His breathing picked up, going quick and shallow as she described nightlock poisoning, his shoulders hunched, and his hands curled into fists. This was calculated, he could tell, to deliver as much pain as she possibly could, and it was working. It wasn't just a knife she'd slipped between his ribs, it was a knife she'd twisted brutally, hard enough to make him scream.
When she finished, Steve was quiet for a long few moments, a subtle tremor running through him. When he finally spoke up, his voice was hoarse, like his body was locked up too tight to allow him to speak with anything approaching ease.
"If you think that doesn't keep me up nights," he said, "that I don't wish it'd been me instead..."
He finally raised his eyes to look at her, and his gaze was burning but his face was hollow, haunted. "People in the districts die every day because they don't get enough to eat," he said. "I know you know that. There are factory accidents that kill dozens, mines that collapse with workers trapped inside, fishing boats that capsize - and then there are the 23 children the Capitol tortures and kills every year." He took a slow breath, drawing himself up straighter. "I've seen men and women sell themselves to Peacekeepers so they can put food on the table. I've seen people whipped for minor infractions. My mother died because she couldn't afford medicine when she got sick."
"I've got blood on my hands," Steve said. "I'd never deny that. But I won't apologize for standing up for what's right. Stane and his people are swimming in blood, and as long as they're in power, they're going to keep using and abusing anyone they want, murdering children for entertainment, killing anyone who stands in their way."
He probably should have just left. He didn't actually have any hope that he was going to succeed in changing Natasha's mind about any of this; she pretty clearly wasn't ever going to agree with him that things needed to change. Erskine's death, the situation in District 8 - they weighed heavily on Steve, but not enough to change his mind that rebellion was necessary and inevitable.