“It makes perfect sense if the cherem wasn’t on a specific person or people, but on anyone who conducts themselves a certain way.”
1) Are you asserting that the GRA’s cherem was not against specific people but rather was placed against all — unspecified — people who conduct specific activities?
2) If so, do you assert that the GRA intended his cherem to remain active indefinitely, for hundreds of years? Rabbeinu Gershom specifically specified a time frame on his cherem. Do you assert anyone who can place a cherem has the ability the place a cherem that remains active for doros doros?
3) If you assert all the above is true, who do you believe today has the ability to formally pronounce which people today fall into a cherem issued hundreds of years ago? And which such entity has pronounced which people today fall into the GRA’s cherem? And who can dispute such a pronouncement?