My gradeschool years ended less than 20 years ago. There were certainly instances where a teacher's name might change, a teacher would be picked up after school by a spouse, or other incidental clues would give away details of their personal lives, but there there were no direct disclosures or "getting to know us better" when it came to our personal lives or theirs.
We were minors. They were state actors (I attended mostly Canadian public schools) specifically appointed to educate us, not socialize with us. There were strict professional and social barriers not to be crossed, which protected the teachers, protected the students, and enforced the all-important divide between teachers as authorities and students as subordinates, which became especially important in the later grades when teachers may only have been 4-6 years older than the students in the class.
There were no slide shows of Halloween parties, discussions of family lives, or friendly student-teacher chats over coffee. School was strictly about education. Any of these would have violated the code of ethics.
Now... I know US public schools aren't exactly the envy of the developed world. Possibly your ethical standards aren't so rigorous either. But speaking from my own experiences in Canadian public schools, these were the rules.
It's not about what a student might learn incidentally. It's about maintaining personal and professional barriers (as already mentioned) and ensuring educators can't bring the irrelevant, sometimes compromising, sometimes immoral, sometimes scandalous detritus of their personal lives into a classroom full of other people's kids. It's unprofessional and it's a liability.
I have no doubt that if this case was a teacher showing off slides of her church picnic, regardless of nonswhether she was proselytizing, most of the people here would be on her like white on rice for crossing that boundary--and, they would have a valid case.
