Mistwell
Crusty Old Meatwad
There are those who consider D&D's use of the "evil from birth" trope as a cheap cop-out, to avoid considering the ramifications of the player's desire to just kill some monsters.
It's an excuse, but I don't think it's a cheap one (which implies no thought was put into it) or that it's a cop-out (which implies a negativity to the excuse). I think it's done because it's a game, and considering ramifications on that level doesn't match well with the purpose of a game intended for fun. I think there are much better settings for such contemplations, like a class in philosophy, a round of intercollegiate debate, a coffee house session with friends, certain theatrical productions, some poetry, some novels, etc.. But a fantasy game intended for fun doesn't seem like a good match setting-wise for that sort of philosophical debate on a more regular basis.
At least, that is how it's been for my games and experiences. I loved talking philosophy in debate and in law school, but I would not enjoy it on even a semi-regular basis for my D&D games. It's too exhausting, too real,and not as much fun as other things the game offers.
I admit to leaning to that desire myself, but I've thought about it. Is the fact that something is evil by nature enough justification to kill it? The salamanders in this example aren't actively preying upon humans for food or brood-stuff, they're just - I don't know, it's not in the description - greedy and cruel?
We don't have a dragon book out yet for 5e (if we ever will), but the 4e Draconomicon for chromatic dragons made it clear they are born already knowing they are superior to humanoids, already inherently predatory, and already (in the case of the red dragon wyrmlings) having an overwhelming desire to consume fresh meat and kill things and horde treasure. It also goes on at some length to explain that many types don't get this from a society, don't even really have a society, and are simply born with it. Finally, they explain that dragons simply do not think like humans, and it's a mistake to assume they do think like us - their brains inherently work differently than ours.