

Your assumption is incorrect; birthright citizenship is not the only way to become a citizen. Those who are naturalized through means other than by birthright, and all of their offspring, wouldn’t be affected.
For example, my wife became a citizen after immigrating here. Her daughter, born after my wife was naturalized, would be a citizen automatically because she was born to a citizen. Birthright citizenship is not a factor in this example.
Likewise, I would not be affected as my ancestors naturalized through whatever process existed back then, not birthright citizenship. Their children (my great grandparents) weren’t citizens because they were born in the US, they were citizens because their parents were citizens.
There’s basically two methods worldwide for children to become citizens easily - you’re born there, or your parents are citizens from there.
You’re born there:
https://en.wikipedia.org/wiki/Jus_soli
Your parents are citizens:
https://en.wikipedia.org/wiki/Jus_sanguinis