This is a topic quite close to me, as my maternal grandfather and his family were all Bihari Muhajirs, whilst the rest of my family are all native Bengalis. Yes, Biharis enjoyed many privileges during the East Pakistan era, and I understand that this caused much resentment from the Bengalis who faced cultural and ethnic discrimination at the time. However, of course 1971 brought attempts at genocide, and then counter genocide to both groups, the climax of the tension between the two groups. Members of my own family were forced to evacuate the country, whilst other parts of my family joined the Mukhti Bahini, an odd parallel. However, I am not one to believe in dwelling in the past and past events, and I'm glad that the Bangladeshi government chose to allow all descendants of Biharis born after 1971 claim citizenship, however that is not enough in my opinion. Yes Biharis took part on the Pakistani side of the 1971 war, however all those, regardless of past affiliation, who have spent their lifetimes in Bangladesh and identify and Bangladeshi should be allowed to do so.
I also believe, Bihari culture within Bangladesh should be allowed to exist without the same cultural persecution Bengali culture faced in the East Pakistan era, not wanting Bangladesh to be hypocritical to the ideals it was founded upon. Whilst of course, it has become ever smaller, it therefore represents even less of a threat to Bengali Ethnic hegemony. Biharis can be proud Bangladeshis too if they feel accepted and welcomed by their almost century long homeland.