Western countries are increasingly allowing organized Khalistani protests, which experts say is giving them diplomatic leverage while slowing India's progress.

On India's Independence Day, Khalistani supporters vandalized the Indian flag near the Indian embassy in Toronto. Similar protests happened in the U.S., Australia, and New Zealand, all organized by Sikhs for Justice, a group banned in India.

This isn’t new; such protests have been happening in Canada and other Commonwealth coun...