That attitude, while perhaps more comfortable in some ways, just enables the sort of behaviour you encountered, and apparently disliked, from that woman.
A blunt response like, "Fuck off. Don't talk to my son.", followed by walking away from her, may have been harsher and not particularly polite, but perhaps it'd cause a person like her to avoid such meddling in the future.
Depending on where you are, she might have gone decades without any kind of resistance to her behaviour.
Too much politeness can be worse than none at all.