If I shoot you in the head and you survive by pure luck and become a savant would you thank me for shooting you?
I can do you one better

If you shoot me in the head and I survive by pure luck and become a savant - then because of my powers save the countless lives including my family and children - would I NOT thank you?
We can go in circles about a piece of literary fiction probably not to be nominated for Hugo award this year.
As it is, this event (Kim vs Mom) was conceived to be one of the main story drivers and the MC internal struggle to adapt to the change - one of the key motivations.
Again I applaud your opinion and think nothing is wrong with it
That's the another problem, Julie didn't remarry, she grew her children alone because of that. By changing pass, you literally destroyed Julie MC knew about, she is his mother just purely by fcking DNA. He lost all of his memories she shared with. She is basically clone of his mother. This is why I despise Back to the Future series. New family is not the family he knew. Also quick note; already pregnant means nothing, Julie just could have abortion because she wanted to have new family with MC's teacher.
Julie did not marry in the original timeline, her hardship stems from being a single mom. I agree that such change in circumstances would affect Julie's character, probably making her more positive, but MC will miss on all that "good times" and be marooned in a non-existing timeline. As answer to your quick note - 20 years back an abortion may have been harder to perform, and having a loving and supportive partner (Penny) would steer Julie immensely towards keeping the children (as they cannot have their "OWN"). SO we can go in circles here too.
Main question is - since MC's main motivation is for his family to have better life (specially his mother) would he sacrifice it for "correcting" the timeline?