YOU don't belong

Recently, I had someone tell me that I wasn't as "much of" a member of a genealogical line because I didn't have the same last name as the ancestor we were both researching.
It went something like this:

Me: "So X Harding married my Grandfather and moved to Michigan."

Them: "So you're not a Harding then?"

Me: (registering confusion) "Excuse me?"

Them: "You're not a Harding then, because your grandma was a Harding, not your grandpa."

Me: "How does that make me not a Harding?"

Them: "You don't have the name, so you're not a part of the family anymore."

Me: (Stunned silence)

WHAT?

This makes no sense at all. I'm female. If I get married, does that mean I'm no longer a "part" of my parents family? I think my mother would argue that I'm still her daughter regardless of what surname I have, and moreover, I think she still considers herself her father's daughter, even though she has my father's name.

Moreover, if I share a common ancestor with another person, and neither of us have that name, does that mean we aren't a "part" of the family line? Should we then not even bother with any maternal lines, because, after all, we aren't a part of those families?

And furthermore, as an unmarried woman, should I NOT bother researching my father's line, since eventually I will no longer be a "part" of that line?

Seriously, where do people get these theories? Why does it matter what my last name is when researching family HISTORY? I'm as much my great grandmother's ancestor as I am my great grandfather's. DNA and genes hold that truth to be self evident.

Stupid people shouldn't be allowed to do genealogy.