I assert that the reason for the edit privilege is for fixing grammar and spelling. Removing sections of someone's answer you disagree with or even think is off topic is both bad etiquette and an abuse of power. That's what the downvote button is for.
I don't agree that the information was off-topic -- the OP clearly asked about the context of a parent with a newborn baby.
At worst it was extra information, more than was asked for, but in no way was it a problem or tangential or unrelated. And since when is going "the extra mile" to answer a question ... bad?
I would say the edits were probably more invasive than they should have been -- but that's OK, that's why the "rollback" function exists... thanks for bringing it to meta to discuss.
The FAQ says:
When should I edit posts?
Any time you feel you can make the post better, and are inclined to do so. Editing is encouraged!
Try to make the post substantively better when you edit, not just change a single character. Tiny, trivial edits are discouraged.
I agree that you should not edit something you just disagree with. I think removing off-topic information from an answer makes it substantively better.
It's not the first thing I tried, by the way. I put in a comment that your content was off-topic and belonged on the parenting site, but you continued the off-topic conversation you started and showed no inclination to do anything about it. So, I used the privileges I have to improve the site.