Everyone who says that the perfection of the human being is impossible have never tried, thus they are acting just as the contemporaries of Boltzman and Einstein who derided their advanced understandings of the universe. The reality is that most people never try to better themselves, especially if the techniques suggested stray beyond their preconceived notions of the nature of the universe and themselves. As well, most people are caught up in their desires for pleasure and material wealth and generally have no concern for those outside of their social circle, be it based upon ethnicity, form of religion, class, sexual orientation or gender identity.
That the incremental perfection of each human being is possible is provable simply by noticing that every choice we make can be better chosen each day, by conscious thought and honest self-reflection on our past deeds combined with earnest study. We must consciously shift our societies' dynamics from destructive competitiveness to constructive cooperation, from selfishness to selflessness, from callous indifference to caring compassion. Love is the essence of humanity, without such agape (service-based love for all other human beings) we are left as the unenlightened animals we all begin as. Only we human beings have the ability to consciously rise above our foibles.
It is also our nature to require an inward connection with our Creator to effect our transformation from selfishness to selflessness. There is a science of spirituality that is beyond any form of religion but most modern scientists deny such science for lack of external evidence. The evidence must be perceived within oneself, just as Boltzman and Einstein's contemporaries needed to read the papers and understand the processes that they were describing. The difference is that denying the spiritual path indeed makes it not exist for that person, for each person must embark on that endeavor themself before being able to feel its reality. Those outside of that circle of understanding must have an open mind and heart to enter that circle or else they will never experience it and that is just another aspect of our human reality: we are free to choose to remain ignorant of it, but we all know what history says about Boltzman and Einstein's deniers.
"The Way goes in." --Rumi