You can take this too far.  As some have said, there are sins that should not be explored and depths that should not be breached, depending on your stage in life.  There are sins I would not attempt to portray (even to ultimately refute) though the eyes of my MC.  Some of them I might handle distantly through a secondary character; some I wouldn’t touch at all.  They just aren’t things I should be dwelling on right now.
But drawing back, the fact of the matter is:  We’re all sinners.  We all have evil “present with us” in our sinful flesh.  We sin, and believe we’re right in doing so – and so do our characters.  In most stories, chances are, even the MC has a fault they are dealing with.  Many of us wish to make a point with our stories.  We want to refute a sin, show a better way – somehow drive a lesson home.  And if we want to do that organically and naturally, avoiding preachy dogmatism, then we have to portray our character’s sin as pitiable and realistic.  We have to show the audience why the character is doing what they are – and the audience has to believe us.
Recently I studied theme with a screenwriting mentor, and we explored this topic greatly.  When you look at a well-crafted story with theme in mind, every character is struggling with the theme in one way or another – even the bad guy!  The bad guy is, in fact, a very strong player.  On the surface he may seem purely wicked, but when you break it down in terms of theme, you see that he’s actually struggling with the same problem the MC is.  The power of the antagonist lies in this – the antagonist does the wrong thing, refuses to learn his lesson, and fails.  And when the antagonist falls, the writer shows the audience that his way was wrong.
Here’s some of my mentor’s words.  I think they’re very helpful to this topic, in the area of portraying sin realistically.
Quote:
“Take your theme and turn it into a thesis – the point you’re attempting to prove.  For example, if your theme is “taking recognition,” as is the case with Disney-Pixar’s Ratatouille, your thesis might be “You should give recognition where it is due and not take the spotlight for yourself.”
Now flip that thesis around into an antithesis, a counter-argument.  Why, or how, would someone logically oppose your thesis?
In the Argument school of thought, everything in a film relates to the theme.  Every character, every single narrative element, explores your thesis by supporting or contradicting it.  The goal of a story is to prove your thesis – by using the antithesis.
Remember - "a hero is only as heroic as the antagonist is strong."  Most people - especially most Christians - write the antagonist (even if the antagonist isn't a person but just a force) as weak and simplistic and easily overcome.
As an example, whenever a Christian proposes to me an anti-abortion story they want to write, I propose that the story cannot be effective until the writer can create an emotionally and intellectually compelling argument as to why the doctor providing the abortions has a cogent, moral position that is defensible.
The reason is for this is:  You're going to have your main character, for most of the film, unwilling to confront the truth of your premise.  In effect, your main character is going to be saying to himself and the audience "The antithesis is the right way.”  If the main character can’t prove to himself (and the Audience) that he might have a valid position, it's all just tripe and melodrama.
The problem with most faith-based filmmaking is that people think of a problem that "other people have" and have a simplistic solution to that problem and then assemble a simple narrative to illustrate that fact.  What you want instead is to find the emotional core of your own struggles with accepting the thesis and weave that into your main character.  So as he's making the choices that lead her deeper and deeper into trouble, the audience will either think "but he's doing the correct thing!" or "man, I understand why he's doing that, but it’s not right!"
In fact, the strongest position to take is to establish, narratively, that the worst choice your main character could make would be to accept the thesis!  And then you elevate the story by inverting it at the end, so through the prism of the climax we see that he - and we - were wrong all along.
Of course, in order to do that, you'll have to establish that your character’s choices all along the way are the natural human and good choices and perspective, but that there is a Better Way.  To accomplish this, you need to discover the common, human reasons why we would go against your thesis, so we understand why your main character does.”
In effect, if you want to teach a moral organically, you have to look at your own sin.  The logic behind wickedness is right with you!  But you have been shown the better way.  And you can use the two together, the knowledge of your past sin and the light of God’s truth, to bring others down the same path.
All of that to say – you can take it too far.  By no means am I encouraging you to explore dark sins your spirit is not ready to tackle.  But I am saying that looking at things from the antagonist’s POV is not necessarily that unusual.  It depends on how dark and how wicked you start him out as – and what your end goal is.  The darker he is, the harder it probably is to portray him as pitiable.  But if your goal is to start with a sinful character and have him gradually realize his wrong… well, that’s what you do with all your characters!