Dude, I've likely been playing since before you were born.
WTF?
I cut my teeth on AD&D and BECMI in the early 80's.
Well done. I GMed my first game in 1982. What difference does that make?
I've literally played at hundreds of tables across nearly 40 years and three continents, across 5 editions of the game (skipping one).
PC's with 'Good' on their character sheet, and then proceeding to be very Evil (and then attempting to justify it to the DM) is not a rare phenomenon. It's actually incredibly common.
I've played at tournaments, in club games, and with friends. I've read accounts of people's play in the columns of Dragon magazine, on usenet, and on message boards. It's not a phenomenon that I've ever personally encountered. When I see it mentioned by others, I regard it as a sign of degenerate play: either the players are 13-year old boys or thereabouts who need to develop a bit of maturity, or else something is going badly wrong with the whole game setup.
Our game rewards violence. Literally. With XP. Its the game currency to advance your character. Killing things and taking their stuff is the central core of the game.
I have not played a game of D&D that fits this description since about 1984.
Katharine Kerr had an article on awarding XP for achieving goals beyond dungeon looting in Dragon 95. The most recent game of D&D I played that was more than a one-shot was 4e, which (i) does not depend upon violence to advance, and (ii) does not treat looting as the principal source of treasure. Default D&D does have magic items as a central element of PC build; in my game these were mostly gifts (from NPCs or gods). The last time I was a
player in a regular game of D&D was in the late 90s: the version being played was 2nd ed AD&D, and killing things and taking their stuff was not central to that game.
The game is built around violence, with abilities having mostly combat effects.
4 colour comics are built around violence. That does not mean that they celebrate psychopathy. It's a medium, not an end in itself: Hulk vs Thunderbolt Ross, Banner and Doc Samson is the Id vs Ego, Superego and Therapist. The violence is just a storytelling device.
In the same way that it is trivially easy to have 4 colour comics without murder or torture (I give you the history of Marvel Comics at least until the mid-90s), so it is trivially easy to have FRPGing without murder or torture.
Look at any alignment thread (including this one) in the history of the internet, and you get two clear camps form:
1) The ends justify the means and Lawful means following the laws. These are the dudes that want to apply a Chaotic Good alignment to the Punisher.
2) The road to hell is paved with good intentions, and 'Lawful' means following a strict code of conduct - not necessarily the law of the land. These dudes (and I am one of them) rate the Punisher as LE.
You then see the twits in Camp 1 start to condone even genocide, murder, torture, filicide, infanticide, mass killings etc as something a 'morally good' person can engage in, and the argument grinds to it's inevitable stupid and pointless insults and madness.
Every. Single. Thread. And nearly at every single table of new players I've ever had (and I've had hundreds of groups).
Who in this thread is asserting that genocide, torture and killing children is a good thing?
Of course it seems to be not that uncommon for GMs (i) to put pressure on their players to play Good PCs, and (ii) to set up situations in which it effectively infeasible, as a gameplay move, to spare the Orc children (or whatever). This is trivially easy to avoid by changing the fictional set-up. It doesn't tell us anything about the moral character of the players; it tells us about the lack of skill of the GM.