But what happens if you go too far? What if you end up making a antagonist who is sympathetic to the point that you actually care more about their plight and agree more than their point of view than the supposed good guys?
It's a tricky one. And I will say right off of the bat that this is not always a bad thing: having a plot develop in a way where the tables are turned and the reader begins to identify more with the villains than the goodies makes for a fascinating and challenging read.
But, in conventional terms, titling the reader's sympathy in favour ultimately harms your reader because when it comes to the resolution and your villain is defeated, your reader will feel deflated, that true justice was not meted out, and the so-called protagonist ultimately ends the story with blood on their hands as a result of damaging the desires of a sympathetic character. Now again, that may be something that you're aiming for, and it would certainly make for a clever twist. But for the sake of argument let's say that we're putting together a story with a standard protagonist-antagonist dynamic here.
The key thing to bear in mind is that there is a big, big difference between liking a character and sympathizing with them. Ultimately, your antagonists can be likable, dynamic and even understandable, but the reader should never, ever really sympathize with them. Your antagonists may claim to be freedom fighters who serve the interest of the common people, and their leader may be charismatic and sport a great sense of humour, but if they stoop to murdering the people they claim to protect and frame the murder in a way that they can blame it on the evil Empire, then you have just created an effective antagonist. Understandable? Perhaps. But never, ever sympathetic.
An excellent example of this is Die Hard. Hans Gruber and his band of terrorists hold the Nakatomi corporation siege, with the aim of teaching them a lesson about corporate greed. Okay, now so far we have a protagonist that we might fall into the danger of sympathizing with. After all, isn't the idea of bringing a greedy business to its knees something that is darkly appealing to most us? We may not like the way Hans does it, but in theory it's an idea we could get behind.
But then the movie takes steps to rectify this. The first, minor step is when Hans reveals that the whole 'terrorism' thing is just a front, and they are just trying to steal the money. So, we have stripped away that concept of them being terrorists with a conscience: they're just straight up theives. But hey, they're still stealing from a big corporation, aren't they? And we have no reason to like corporations. So we can still just about sympathize with Hans and his crew.
And then it happens. Hans straight up murders Joseph Takagi, the 'face' of Nakatomi in this movie. In this one stroke all possibilities of sympathizing with these antagonists is gone.
Because all effective antagonists need this moment: this 'Point Of No Return'. The point where they do something so abhorrent, something so I relatable to the audience, that their comeuppance from the protagonist will be justified.
Because just imagine for a moment of Hans and his team had remained those terrorists bent on teaching Nakatomi a lesson in corporate greed all the way through. Imagine if Hans had not killed Takagi. Suddenly we don't want to root for John McClane quite so much because, deep down, we kind of want the terrorists to win. They have not hit a Point of No Return so their motivations can still be sympathized with. In this new version of Die Hard, McClane's victory will feel off, because the story is longer about a guy who fends off a group of hypocritical theives and murderers, but is now a story of a cop dealing cold hard justice to a ragtag bunch of people who had a sympathetic, if radical, aim in mind. And that just would not have worked.
When an antagonist passes a Point of no Return, they are beyond redemption. They could be remorseful of their actions, they could try to repair what they have done, but the damage a Point of no Return does is irreparable. It's the reason why so many people, myself included, take issue with Anakin Skywalker's cold-blooded murder of the Jedi children in Revenge of the Sith: killing one child is unforgivable, let alone a whole room of them. This effectively sours Darth Vader's redemption in Return of the Jedi, because it is a redemption that he, quite frankly, does not deserve.
Antagonists can be many things. There is no singular template for one. But in order for your protagonist's quest to have meaning, and for the reader to sympathize with their plight, a key factor is to make sure that the protagonist isn't one they can side with. Achieve this by giving the protagonist a Point of No Return. Even if they ooze charm, it will be a antagonist that the reader loves to hate.