Okay, outsider meta POV here. I've never seen DA. I wasn't that interested when it was on. But I've checked out a couple of clips of JA since SPN. He looks so young there.

Just my two cents from having heard about the plot second hand, but: Alec looks like Ben, and from what I understand Max thought of Ben like a brother (even if he was crazier than a fish in army boots). So when Alec shows up, acting skeezy and wearing Ben's face, Max has more than a little hositlity toward him.

Like I said, individual mileage may vary.