And what's the alternative to not killing or defeating enemies in many games? Just avoid them? That's bad in most circumstances, and is in fact near impossible in many games.
Remember we're primarily talking about offering
variable xp based on playstyle (e.g more xp for non-lethal than anything else, more for headshots etc). But OK, as you wish:
Why rewarding even the same amount of xp no matter how you take out enemies is bad in an RPG offering variable playstyles (using Deus Ex as an example):
-It encourages taking out neutrals turned hostile. Starting fights with police just for their xp, for example. Sure, the designer can exclude police from providing xp rewards (HR did this if I recall), but a player will only discover that after having killed/K.O'd the police in the first place, and it creates additional inconsistency (even if only minor).
-It excludes ghosting/avoiding enemies.
-You associate NPCs with xp, a unbelievable award. Hostile NPCs only, at that. they have a subconscious asterisks above their head
*comes with 10xp for removal. It influences how the player perceives the virtual entity on some level, which is bad in games that intend to be immersive.
-Frequent pop-ups per takedown (if present) are potentially annoying, and also are used to confirm kills/K.Os. In other words, immersion breaking.
-Does it account for friendly fire or suicide? If an NPC accidentally killed his buddy or himself, why do I get the xp? and if I don't, that rules out emergent (unforeseen) scenarios where a player may have set it up to happen.
-Does it account for your team mates killing the enemy? Picture Jojo vs Renton. If you do not get the xp for renton killing Jojo, that strongly encourages the player to take out jojo himself. So you make it so it does give xp for it, at some point. We get xp for giving our gun away and doing nothing now!
I could go on, and I will if I feel up to it later.
And what's the alternative to not killing or defeating enemies in many games? Just avoid them? That's bad in most circumstances, and is in fact near impossible in many games.
Deus Ex can be ghosted in almost all instances. You don't have to ghost the whole game, you can just be low on resources and want to avoid a particular group. Or you may take pity on an NPC based on his dialogue and not want to fuck up his day. Roleplayers and bleeding hearts will relate.
No xp for specific actions is entirely choice and playstyle-neutral, as is xp for exploration. It only excludes non-explorers, yet there's no reason not to encourage exploration and if you're not exploring you're playing it wrong, or are speedrunning, speedrunners being something that designers should never take into consideration in an RPG (and most other types of games that are not about racing against the clock).
Most of this applies to killing or defeating enemies too. The reward you get from that is a sense of having overcome them, or having engaged in a good fight if the combat gameplay is good. In addition, it also frees up a space and makes it safe for you to look around or take a breather if you feel like it.
Those are things that cannot be helped, except by making combat more shit by design for example, which should never be a goal, and most are are natural sense of reward anyway.
They're also mostly a sense of reward and not actual virtual-material rewards like xp is.
As for being on your case, well you know very well that you've had a sordid posting history and you have got into nasty fights and arguments a bit too often because of your aggressive posting. I just try to warn you against that.
Sordid or not (no), I don't intend to change.