the more I think about of the Devil, the more I feel that one of its core themes—arguably the core theme—is that deciding why you should fight for something and deciding how to fight for it are two very different things.
on a surface level, this is what makes Morgan such a good lawyer. most obviously, she goes into every case with the mindset that she automatically believes her client isn't guilty, as she makes very clear. but she also chooses her cases in the first place (or in episode 2, chooses to put actual effort in) because she genuinely sides with the accused, even before it's good courtroom practice to do so. she knows David well enough to doubt the idea that he'd commit suicide; she comes to care about Serra (regardless of her own refusal to admit it) enough to believe that she doesn't deserve death; and she intuitively believes Sosuke didn't kill Chopin because it doesn't fit his character.
Serra's case is particularly interesting, though, because the evidence is so damning that Morgan arguably doesn't believe she didn't commit the crime until later on; instead, she stands up for her because she believes Serra doesn't deserve the punishment for the crime, regardless of whether her physical body technically committed it. the fact that Morgan even thinks about the consequences of a ruling is in stark contrast to basically everyone else she works with. London, Reyes, Aidey, and especially Emma are all content to assume that the system works: that their role is only ever to determine guilt, not punishment. even Morgan's own clients don't always care—Sosuke has to be talked into seeing how awful imprisonment would be. it's only really Serra herself who seems to share an interest in what happens to the guilty.
none of this, though, affects how Morgan approaches the actual trial. maybe it gives her a little more conviction, but considering the way she'll gladly go all in even when she has no real thread of evidence to follow, she seems like she'd display just as much confidence even for a client she knew to be 100% guilty. getting at the actual truth of the matter, the character traits and motivations that convince the protagonist of their client's innocence, is often a theme in detective games—but to Morgan, it's an afterthought, because the legal system she works in doesn't give a shit about anything but cold, hard evidence. in this setting, the only kind of argument that matters in court is one of cold, black-and-white logic.
Morgan understands that perfectly, and acts accordingly. this, I think, is what makes the analogy of gambling for her courtroom strategy so fascinating: it's not just that she takes wild risks, it's that she knows only the outcome matters. she's not fighting to be right, to have the better hand, to prove what she believes—she's fighting to win, and if you play your cards well, you can do that without being right at all.
it's very hard to guess where the story is ultimately going with regard to its moral judgement of Morgan—because, really, how do you resolve her arc in a satisfying way?—but my best guess is that it has a lot to do with this. the evidence against her is beyond damning, it's inarguable; we see exactly what she does, so clearly that it can't possibly be waved away. if someone who only cares about determining guilt, like almost everyone in Morgan's life, saw the whole picture? they would convict her in a heartbeat, and probably never think for a moment about the consequences of that ruling.
there's someone in Morgan's life who's starting to see things the way she does, though. someone who's learning that getting the right outcome is a very different thing from demonstrating the truth. you might think about that thing if Morgan had, say, gone all-out to prove you weren't a person, knowing that it was false, but also knowing that it was the only way to save your life.
to Serra, what happens to the guilty matters. what would happen to Morgan, if the case against her was clear, matters. and even if all the evidence in the world proves her guilty, because she is, I think Serra will find a way to "prove" it wrong. she believes everyone, even a murderer—even the woman who killed David, and the man (she thought) nearly killed Morgan—deserves a second chance.
and Morgan, despite herself...has taught Serra exactly how to give her one.