Mathanxiety, you really do need to give teachers a bit more credit here.
There is quite a continuum between behaving like a perfectly normal member of your students' extended social circle & sharing 'inappropriate' detail.
Eg. dh drops me off at school this morning. Lots of students see this happen. Some of them ask questions like: Was that your husband, miss? Your dd was waving to us, how old is she? My sister's at [Local VIth Form College], miss, she says their drama technician's in your husband's band, are they any good? etc etc etc.
The sky's really not going to fall if they know the answers to any of these, or if I attend the evening Christmas concert in a couple of weeks/next school-organised trip to local rugby team's away match with family in tow - as we are encouraged to do.
There is an enormous gulf between 'students know the same sort of information about my life outside school as my colleagues do' -cf. the teacher in the OP & her civil partnership - & 'I promote my own views on whatever controversial subject matter it takes my fancy today to proselytise on'
We have really quite effective professional guidelines, & in the vast majority of cases, we're more than capable of exercising good judgment.
The whole 'What if was teaching your children?!' motif is more than a little disingenuous. There are occasional nutters in teaching. A teacher choosing to share unremarkable personal news doesn't become one of them.