I think Swami Ramdev is referring to the menace posed by the uncontrollable eruption of population among Muslims. We must also understand that he is trying to solve a problem that the Muslim community is well known to create. If their population continues like this, Hindus will become minority in our own country. Not only that, Muslims will vote for Muslim politicians and they don't care about Hindus or any other religion as history and real-world data clearly show. Until the time Islam takes over major Hindu areas, they will go hand-in-hand with Christians. Once they find the opportune moment, they will also war against Christianity as they have done since centuries.
The collateral damage that will take place in their war will be our people, our history, our culture, our heritage and our value system. It may sound very dramatic, but if you would have told a Hindu living in Lavapuri (old name of Lahore) in 1930s that very soon he and his family will be wiped out by radical islamists in 15 years, he would have laughed at you. But we know what happened due to their massive rise in population explosion - they demanded another country - and in the process, massacred lakhs of Hindus.
I see people laughing in the same way here today mocking Swami Ramdev, but they don't realize the kind of danger not only our people, but our entire civilization faces if Hindus don't unite and fight against these regressive, barbaric cults like Islam and Christianity.
Islam and Christianity don't respect other religions like we do. Either convert or die is their defacto standard of operation throughout centuries.
My humble request to all the learned members of this group - please look at the bigger picture, please read real history before making comments that are out of touch with reality.