Abigail isn’t against the fact that John going to Kill Micah
She’s against the idea of allowing John to sink back into his old life. This is shown throughout the whole epilogue where even after he did the smallest thing by getting back the other ranches goods from those thieves it made her angry, or how she didn’t like the fact that he was helping Sadie hunting bounties. She doesn’t want John to go out and cause trouble because of how hard it’s been for them trying to start a new life after dutches betrayal. It’s made clear she wants John to make himself by doing honest work.
She finally she’s that when he buys the ranch and builds the home only to see it possibly slip away. It has nothing to do with Micah being the father, which I strongly doubt is. There’s no evidence to back any of the claims.
John acts the way he does because he still sees himself as a kid. There’s a huge difference in personality between jack in 1 and him in 2. I see this talked by many how John isn’t the father cause he doesn’t seem to care. Again
Also Abigail was the camps prostitute.its been stated plenty of time that everyone’s had their way with her, Dutch even says so in rdr1.