Depsite your racist sentiments I agree with you. Bangladesh has essentially become India's Frankenstein. What we couldn't do militarily, they did demographically. In 4 or 5 decades, WB and Assam will be fully Muslim majority. Kudos to them.
You are mistaken. There is no large scale Bangladeshi Muslim migration in India. There are millions of Hindus in India who have ancestry in current Bangladesh, they are victims of partition. So when you hear the term about 10 million or 20 million Bangladeshi in India, it can only be them. But sanghi scumbag propagandize this number to be Muslim Bangladeshi which is entirely false. West Bengal and Assam's muslim population growth rate is in line with all Indian average Muslim population growth rate. In fact if you compare, Urdu speaking Muslims in Bihar and Uttar Pradesh has higher growth rate than Bengali speaking Muslims in West Bengal and Assam.
But West Bengal and Assam's Muslim population captured the Hindutva attention because in these two states, Muslim constitute a larger minority and they form majority in some districts adjoining Bangladesh. Those Muslim majority districts are the Muslim majority areas which were not given to Bangladesh during partition but awarded to India. So from the start, West Bengal and Assam has higher Muslim percentage than other Indian states. And in the last 70 years, this proportion risen even farther because of higher birth rate among Muslims. West Bengal and Assam Hindus have significantly lower birth rate than Muslims, even lower than all Indian average Hindu birth rate.
But this birth rate differential between Hindu and Muslim communities in WB and Assam is rapidly diminishing. So contrary to your assertion, West Bengal is not going to turn into Muslim majority ever. At most Muslim proportion will continue to rise up to 35 percent of total population in West Bengal from current 28 percent and then converge with Hindu growth rate. Assam is somewhat less certain, they already have 35 percent Muslim, so there is a possibility that they can go very near to the 50 percent mark or even cross the 50 percent before stabilize. But whether Assamese Muslims are 35% or 45% or 55%, does not matter because they are loyal Indian citizen and will remain so.
Assam already had 25 percent Muslim population in 1951, in the following decades, Hindus there rapidly embraced modern education and family planning, while Muslims remain backward and rapidly multiplied like any other backward communities in the world do. This is the reason why Assam's muslim proportion risen from 25% to 35% in the last 70 years. It is not due to any large scale Bangladeshi Muslim migration. Same is also true for West Bengal. West Bengal Muslims also socio-economically backward compared to hindus and multiplied rapidly relative to Hindus. West Bengal already had 21 percent Muslim population in 1951, in the last 70 years it risen to 28 percent. And may rise up to 35 percent before stabilize. So there is no Muslim majority West Bengal in horizon. So you should stop blindly believing sanghi propaganda against Bangladesh. Among the three countries, Bangladesh, India and Pakistan, Bangladesh has the most successful family planning program.