A Brahmin is not a brahmin by birth alone. He/she has to nurture the rules,regulations, customs, traditions, foundations, fundamentals and social, legal obligations. In a nutshell what these rules say ? ahimsa, satya, truth and service to mankind in all possible ways and means at any cost. The have to learn a lot and preach to others to behave. Guide the society to good life and help them attain their just goals. So, anybody can become a brahmin if he/she practices these qualities like the King Vishwamithra becoming Brahmarishi Vishwamithra. People including brahmin community started deterioting towards greed and money with conforts. Now those other than brahmins have started to realise that the principles brahmins followed and the way they lived is correct and they started to follow the brahminical way of living. similarly, brahmins who hailed from birth as brahmins started slipping from their genetic hold and crossed platforms for greed. Most of the brahmins today are not at all brahmins as they never practice anything that a brahmin is supposed to do. Some qualities of brahmins which are left out with the born brahmins are, 1. they can never fight back physically 2. very hard for them to tell a lie 3. god fearing 4. accept mistakes and truths when confronted with 5. will be happy with what they have and such things.
Anybody who wants to become a brahmin should learn the vedas and preach the society about good things, truth, tendency to always help others, do not earn money in unnatural ways and means, law abiding, etc etc. I am not a writer that i can put things in a beautiful perspective. Many rishis have converted people who were not brahmins into brahmins and they are guided to live the way brahmins lived. Brahmins who still follow the rules and customs are finding it difficult to sustain way forward similar to the plight of parsis in our country.
If the brahims thus left out try to consolidate their strength and fight then they stand a chance to survive. Those went out of the fold can never come back into the fold as they no longer fit into rules. Those coming in should always stick with the fundamental rules and can never think of going back.