(Sorry about the lack of formatting in this post. On certain computers I can only type in the HTML form and sometimes forget that I need to manually enter the formatting rather than just hitting Enter.)
Related to anger and yet distinct from it, hate is a very potent emotion that should theoretically be quite easy to use in a campaign. After all, many campaigns have some form of Nemesis figure that needs to be taken down a few notches. A fair few also include evil organisations, armies or nation states that the characters wish to dismantle.
Yet how often do PCs really hate the enemy?
How often do they act out of a driving need to see the enemy taken apart rather than simply doing so because "it's the right thing to do"?
Sure, it happens, but not so often as you would assume considering their PCs are motivated to destroy something with violence which is a shame as it's relatively common for people learn to hate the things they seek to destroy even if that hatred wasn't the initial impetus for the destructive impulse. In other words, even if a person aims to destroy something for intellectual reasons or monetary gain, they generally come to hate it because, at the very least, you feel less guilty destroying something that you hate.
So why is it such a hit-and-miss affair with some campaigns getting the PCs invested to such a degree while others have PCs who really don't care much?
Partly it would be due to PC motivations. PCs are generally mercenary types. This is their job. Just like soldiers from various armies, they don't necessarily hate the things they fight. They don't really need to because the fact both they and the enemy are trying to kill each other so it's a bit Quid Pro Quo. It'd be almost hypocritical to hate them. Of course, most of the soldiers on the ground aren't also choosing their enemies. It's decided by politicians, nobility and generals. They're just along for the ride and the pay packet.
Partly it's because the bad guys haven't been given a chance to commit any evil actions. So the PCs are assaulted by bikies a few times. So what? Sure that makes those bikies an enemy, but is it really worthy of hatred to an equally violent group of individuals? Especially if the PCs have killed a few of them and haven't lost any of their own. Fantasy campaigns are especially guilty of this with most PCs happening across wandering monsters from a demonic army or groups of brigands that set upon them when encountered. Sure, rationally you know that regular civilians would have been brutally killed by such people but that doesn't really mean anything when there's no evidence of it.
Partly it's because even if they are committing evil actions, it's often occurring out there somewhere. Even if it's happening around the PCs, the tragedy of the affair is generally avoided as tragedies and traumas are unpleasant so folk often (but not always) skirt around the issues. Sure you might have a dragon killing villagers but that doesn't really impact on players because those villagers are just nameless NPCs. They can't even see them beyond an occasional imagining based on the Storyteller's narration. Even if the Storyteller attempts to characterise the villagers, they might then feel loathe to kill them off so brutally. Those that do might be a little too trigger-happy which means the players see any interesting NPC as a step away from death and so purposefully don't invest in them. They're not real people, after all, they're just plot devices with a ticking clock inside them.
Finally, hatred can be a draining emotion. It's intense and it's the kind of intensity that can burn itself out. No one wants to spend several months burning for revenge against a particular person so generally even if hatred is piqued on occasion, it'll either dissipate or be put on the back burner for awhile when the Enemy isn't front, row and center. There's absolutely nothing wrong with this element. Generally once a player has declared a burning passion for the destruction of the target, that's that. That NPC is marked for death short of a really amazing chain of events.
So knowing all of that, what do you do?
What if you really want your players and their characters to really hate someone?
Well, make it personal. It shouldn't happen to someone 'over there'. It should happen to them or someone close to them. Ideally someone both players and characters like - which can be different to the NPCs the Storyteller wishes they would like. If you want to get them to hate the local thieves guild, have the thieves steal from them. If you want them to despise an army, introduce them to a few villages along the way until they find the one they like and then have them find the village burned to the ground on their return. You don't need to wipe out all of the villagers. It might even be more effective to turn the villagers into refugees and encourage the PCs to escort them somewhere.
Make it matter. It's not enough to do something petty or, alternately, too broad and overwhelming. A monster that wipes an entire country off the map is scary but the players aren't going to feel the impact from it anymore than they would if the thieve's gold stole five copper coins. Ensure that the event is large enough to affect them, such as by stealing all of their gold or selling them dodgy healing potions on the black market which don't work, but make sure that it's not so large that they can't quite conceive of it. If you do go with a truly large event, keep it personal by including a few key details for them to latch onto. Perhaps they knew a few people in that country who disappeared or their favourite tavern lay within it.
Make it believable. Tie it to something that might happen in the real world. Rather than having your mage unleash a demonic horde upon the world and expecting that to engender hate, have them research and unleash a magical plague to terrify the local populace and tap into fears of disease research. Sure you can include the demonic hordes, but unless you find some way to really tap into real world anxieties than it may not flip the triggers you expect.
Finally, make hatred worthwhile. Let their passions inspire other people to help them. Let their enemy be something that can be combated with violence. Show them the hatred that other NPCs feel so that they don't feel like they're over-reacting but also include people who really think the enemy is fantastic so that the PCs have to convince them otherwise. Perhaps even allow an in-game resource such as willpower be regained due to the burning power of that hatred.
You can also tip the balance by subtly altering your descriptions of the person by using hateful terms though take care not to descend into melodrama with a moustache twirling villain who is too silly to be truly hated.
"The noble stands at the parapet before you, slender fingers gripping the railing like talons, yet he smiles at the crowds as he speaks in peaceful terms of a united nation. It is only as he turns away that you notice the sneer on his lips...."
To be honest, I've never tried to make the players hate any of the NPCs although I have always taken notice when they do. It's often easier to simply latch onto things the PCs feel strongly about rather than trying to coax them to care about other situations.