Who are the “people that hate it” when Vietnamese are grouped with East Asians? Who are the people that want to “group” Vietnamese with East Asians? The Vietnamese certainly don’t.
The Vietnamese are from Southeast Asia and consider themselves Southeast Asians. They are proud of their geographic and genetic ancestries.
As a Vietnamese, I never grouped myself with East Asians or had anyone else tried to group me with East Asians. We are Southeast Asians, proud, and we love ourselves!