Hi there! I'm dropping in for BvB :)
I'm glad I stumbled upon this. Stories about the aftermath of the war are a favorite of mine. I could very clearly picture this scenario playing out just as you described; it's believable that a few students would get extremely upset by the presence of the Malfoys in the Great Hall and, by extension, have the nerve to confront them. After spending the entire year under the harsh scrutiny of Snape and the Carrows, I'm sure many of them leapt at the opportunity to unleash their anger and vengeance on those who caused so much pain. I think it's really fitting that you chose Ernie to be one of those students, as he's always had a knack for speaking his mind without always sopping to think things through.
It was true to character for Luna to spring into action after sensing trouble in the most Luna way possible: calmly letting someone know about it. I love how she, along with McGonagall, was a voice of reason when tensions were high. She wasn't dismissive of anyone's concerns and feelings, either, which is so poignantly Luna. And it's fitting that Neville was ready to throw himself in front of a curse in the name of civility.
The question you ask with this story is so important, because even when we want it the most, vengeance isn't always the way. In fact, it usually isn't. Vengeance and justice are hardly equal although they are often treated as such, and I loved that you used this theme in a post-war fic. It fit perfectly!
This was really well done!