Celebrim
Legend
That might have been self serving bias: One player liked to play a mage and didn't want to be restricted as far as what creatures he could summon. (Side question: What happens if a player summons all alignments of creatures?)
I believe that in D&D terms most people IRL are 'Neutral'. They don't really care about issues like 'philosophy', 'ethics', 'morality', or 'spirituality'. None of those things seem to impact their daily lives. They believe that they are basically 'good people' and want to be basically 'good people', but also believe that sometimes 'doing what is right' means making compromises. They believe that morality is basically relative and situational and some things you'd never contemplate otherwise can be the right thing to do circumstantially. They believe that vices are really only vices if you take them to an extreme, and that anything taken to an extreme can be a vice. In short, the 'neutrals' are convinced (like almost everyone else) that they are 'good'.
Obviously, if the player doesn't care about the morality of what he is doing and he's only taking care not to be too extreme or go too far, he's probably neutral. If a wizard has 'neutral' written on his character sheet, and he's selecting creatures to summon solely on the basis of their situational utility, then I think he's in character.
I agree with all of this. However, I have found substantial disagreement from various players, to the extent of complete disagreement and unwillingness to consider the ideas as possibly valid.
I find that about 90% of players are unable, for whatever reasons, to play an alignment other than the one that they hold IRL. Lawful players IRL find they are unable to play anything but lawful characters, because dishonorable behavior (even imagined) disgusts them or seems incomprehensible to them (my most lawful player in my current group is always telling me after sessions when we discuss what happens, "I would have never thought of that..."). This goes around the wheel. Chaotics find themselves unable to abide by rules for long. I've had players completely unable to play anything but an evil character no matter how much they tried, which made me glad that there IRL self only expressed their disposition in generally petty ways and they weren't being asked to make life or death decisions IRL.
I don't pay too much mind to this, but it becomes a problem with a player insists that a certain outlook is 'good' even when it contrasts with the definitions you've provided for the alignments or when a player wants to be the 'hero' and to think of himself in that role but doesn't want to pay the price of being the hero. Additionally, the fact that underneath all of this it is a game tends to favor having the 'Neutral' outlook within the game unless the player explicitly considers exploring morality, philosophy, and spirituality as more important than 'winning' the game (acquiring XP, power, and keeping your character alive). Neutral is above all as pragmatic. So, in general if I believe the player is going to play his character pragmatically, I strongly encourage them to take 'neutral' as the character's alignment to avoid any possible argument. (Then again, you have the player that wants to play evil who also wants to use 'neutral' as emotional cover.)
In general, you should try to avoid the need to strongly disagree over this. If the character wants to insist his pragmatic outlook and lack of willingness to sacrifice immediate interests is 'good', there is little need to argue about it. Except for a few classes, there is no direct punishment for alignment drift. Instead, simply consider the outcomes of what he is doing and communicate the outcome to the character. At that point, it turns from an argument about IRL concepts, into an argument over what happens in your imagined world. And if the player still wants to insist that what you have chosen as the reasonable outcome isn't reasonable and isn't what should happen, then the fundamental problem is that the player wants to be in the game and running it too. He's trying to tell you what NPC's think and how the world should behave, and that should be the point you make to him. Maybe he is being unreasonably persecuted or blamed when he uses necromancy to save the village. Maybe the gods that call themselves 'good' aren't in fact good, and are just a bunch of jerks. Maybe he is the most noble character around, and the foolish village cleric is vain and envious. Maybe the bad things that are happening really aren't his fault. But his character should take up that issue in game, and not make it a point of contention out of game. Your basic defense is, "I told you this is the way my imagined world works all along; this is the way it working."
Just take care to not be letting your emotions about interfere with your judgment. Remember that being righteous, noble, and pure in your deeds generally doesn't lead to everyone liking you and no one disparaging you. Remember most characters in the world are probably neutral too and also believe that they are 'basically good people'. Remember not every failing has a consequence. But conversely, don't let a player behave in a way that doesn't have consequences if you want to have a world that feels real and is worth exploring philosophically. If the player plays a hedonist, there will be consequences. If the player makes no consideration for morality, there will be consequences. It's not a judgment against those actions; it's just the way the world works. After all, it could be the reasonable price for being good is they decide to kill you. Happens a lot. Everything has a cause and effect.
Where you really get into trouble, or where I've seen DMs really get into trouble, is if you don't take the time to make this all clear ahead of time so that it comes up as a complete surprise in the middle of play. Often this happens because the DM has never clearly worked out in his own mind what he means by 'law', 'chaos', 'good', 'evil' and 'neutral' or why summoning undead is evil or if he can't clearly elucidate why it is that way in his world, and just is working with the vague and often contradictory explanations in the text. That can be a show stopper.