I believe the title already gives a pretty good TLDR, but let me provide a little extra context.
I play in a group with two clerics, a rogue, a fighter and a bard (me). It's also important to know that the DM is a player in one of my groups and plays pretty much exclusively lawful good or neutral good characters. I am on good terms with all of the people involved and I don't intend to change this. We're all adults and if this ever gets out of hand I'm sure we'll find a way to talk things out.
Now to the ingame problem. My character started out chaotic good with a pretty strong emphasis on the chaotic part. She's a fey and orderly things go against her very nature. It's usually small things like planting flowers in the middle of the streets or "resorting" some shop shelves. However, due to some not so nice things going on in the world right now, she began shifting a little more towards the neutral side by developing a indifference towards the lives of several faction members in the world (mostly cultists of various evilish cults).
This led to the party steamrolling a bunch of cultists who expected us to pay a toll for crossing their lands with my character hypnotising them beforehand.
Another encounter had our rogue grow tired of a spectator who blocked our way with obvious implications of combat should we ignore him. Our rogue decided to backstab the spectator mid conversation.
I as a player don't really consider these acts evil. Neither does my character. But apparently the DM and at least one of the clerics see things differently. Which in and of itself is not a problem. However, I got wind that they plan to invoke some sort of plot to "make the party repent for their evil ways". And that's where my issue arises. I have no problem with players or characters who want to be a shining example in an evil world and who see the good in everyone. But I have zero interest in playing such a character and it feels like that is what this amounts to.
So, I'll do the obvious thing and talk to everyone involved before the next session. And that's where you come into play. How would I go about this? What arguments might help my point and what am I missing? If shit hits the fan, I am ok with leaving the game and I know that they will accept my decision. But I prefer to avoid this, as I really enjoy the campaign and my characters role in it and in the group.
Going to echo the prior comment. But here's my thoughts:
Was there a "session zero" in which the group's expectations for the campaign and interactions were laid out? If not, it may be a good idea to pause and have this. Sometimes groups who are familiar with each other skip this because they "know each other", but it can still be good on a campaign-by-campaign basis.
When you discuss it with them, try to start by determining why the DM is acting this way: Since it sounds like the DM likes firmly heroic characters, is this just what they find 'cool' or do they actually object to playing / having grey-er characters in their party or campaign? (Same kind of applies to the cleric's player - are they just "playing the character", or is this what the player feels is right?)
Ask if there's been any miscommunications involved. The thing that sticks out as odd to me here, is that the DM clearly seemed to be urging you towards combat with stereotypically evil enemies in these scenarios... but views you initiating combat as "evil"? It's possible something is getting lost in translation.
Since you and the rogue are both clearly enjoying less cut-and-dry characters, express that this isn't just you-versus-them. Or you-versus-cleric-player. Broadly, try to avoid turning this into an argument between people.
This will fluctuate a bit depending on how roleplay-heavy your group is, but consider asking if this could be dealt with in-character. Is the cleric open to having a crisis of faith over working with such "tainted" people? Are you okay with your character sometimes being held back by other party members when they'd like to be proactive, so long as their view isn't changed?