Option D is correct because democracies have successfully eliminated the idea of political inequality by establishing the principle of political equality. In a democracy, all citizens have one vote, which means everyone has equal political rights regardless of their social or economic status. The context clearly shows that democracies have had 'greater success in setting up regular and free elections.' However, democracies have NOT eliminated the other options: conflicts among people still exist (as seen in examples like temple discrimination against dalits), economic inequalities persist (the context states 'inequalities exist in democracies' and 'Democracy can't reduce inequality of incomes'), and differences of opinion about how marginalised sections are to be treated continue (evidenced by ongoing debates and practices). Political equality through equal voting rights is the one area where democracies have successfully eliminated the idea of inequality.