My point of view pretty much IS my characters point of view with some slight differences. However, it was clear from context that I was discussing ethics in D&D, not in real life. I wouldn't argue real life ethics almost ever. No one can agree on ethics so it's pointless to debate it.
I wish I could give you the entire 30 minute long conversation for context, but the truth is, I don't remember 100% of everything said in the conversation. I just know the question that started it was "I found my character had no reason to go on this adventure and no one in their right mind would want to overthrow a government." And I said "well, the woman in charge is pretty evil and as a good character I felt it was good to get rid of her." And he said "you'd murder the leader of a city just because they were evil?" And I said "Yes, I'd murder anyone who was evil if I could get away with it and I thought it would make the world a better place." And from that point onward I referred to myself in the first person for the whole conversation.
But even if I screwed up the context and called him "not good", that's small. I've had 3 hour long conversations on real life morality that I got sucked in that weren't about D&D at all. In those conversations I was called downright Evil by one of my coworkers. Repeatedly. I'm still friends with that guy and I didn't storm out of the room or slam any doors. Because sometimes arguments get a little personal but you try not to take it the wrong way or lose your temper.
I see you're Canadian. I found this surprising as an American. Most Americans prefer killing an evil person if they know they're 100% doing evil. If you were discussing this at work in America, you might get in trouble for discussing politics and ethics, but most Americans would be in your camp. You get a chance to ice an evil bastard, you do it. I'm in agreement with you on that one. Surprised most of your table wasn't. If you were at my table, everyone there would be in complete agreement with you.
In previous alignment discussions, I've had a bunch of my friends admit to being "Neutral" in real life considering how hard it is to live up to the D&D concept of "Good" in real life. I never considered "Not Good" to be an insult. The vast majority of people in real life are "not good".
What it comes down to is that it was clear to me that I was speaking in character. It was clear to my girlfriend who was there and even before I said anything about this afterwards said "I think the problem is that he thought you were talking about him rather than his character. It was clear to me but I think he didn't understand."
And whether or not I mildly insulted him certainly was no excuse to fly off the handle. He could have said "Wow, that was insulting." and I would have apologized for insulting him and moved on. Instead he ended the conversation in a way that left no room for anyone to disagree with him, ruined everyone's day and made all games we play in the future super awkward. I pretty much don't care what I said to him, nothing warrants that response apart from some seriously horrible behavior.
Edit: besides, he insulted me pretty badly at the beginning with "No one in their right mind would want to go on this adventure". I liked the adventure. It was a lot of fun an I Really did want to go on the adventure. Thus implying I'm not in my right mind.
You two aren't agreeable on about anything. Don't even like the same adventures.