Steve wasn't going to correct the angel, as everything he said was true and sensible. Even his turn of phrase was right, and he wasn't about to correct that. Instead he only nodded in agreement, there was no reason to fix what wasn't broken. Even if the one doing the repairs was one who could not be trusted.
The invitation to the hunt was one he gladly accepted, and there was no better way to put training to use than to go out and do the job. Besides, staying to the side and allowing others to defend him and others. Staying in the tower (or his apartment) and remaining idle was not something he could do, it wasn't his nature.
"I'd like that," he replied to verbally accept the offer so graciously given. "It's battle like any other, but with a different opponent and different set of skills. As for earning scars, well..." Steve shrugged and took a drink; if Castiel didn't know the story he was going to get a quick overview now.
"I don't have any scars," he told the man as the smile left and he became entirely serious. "With some medical help I would probably have healed from the fight- help to stay alive long enough for it to happen. What was done... I heal very quickly, I don't get tired easily. I am... enhanced, I guess you'd say. A super soldier." He watched for signs of disbelief, and who could blame the man if he didn't believe? It was a fantastic story, one straight out of a comic book (which they did create once he'd gone to war to actually fight), but Steve knew it was real enough. It was his life.