It is mainly for identification, if they are caught, can be identified & they will be deported easily. Unlike the 20 million illegals who abuse our democratic and judicial processes.Even going with valid visa would not guarantee that they would not vanish throwing away their passport and visa to live in modern slums of Mumbai and Bengaluru disguised as Indian Muslims. They will work as a construction laborer and house maid in rich Hindu houses and will earn millions of Rupees, making 100 crore Hindu a minority in their sacred homeland. So it would be wise, if you can convince the Bajrang Dal wing in Kolkata to beat-up a few among these 1.5 million to create a panic so that flow from Bangladesh totally stop. It will secure India's future as a rich, vibrant Hindu rashtra.
Maybe try being edgy to those who prefer living in slums in India to Shonar Bangla.