What does MILL insist on freedom of thought and expression in on LIBERTY? JOHN STUART MILL ON LIBERTY

In the end, I would say that the fear of "the tyranny of
the majority" is what helps to motivate Mill's insistence on freedom and expression. 
Mill was convinced that the prevailing attitude of liberal political thought of the time
was steeped in popular sovereignty, and then living purely with the results of such a
principle.  In the end, Mill understood that government has to be driven by both
consensus and the need to appreciate the voices of those who might have been on the
lesser end of such decisions.  For Mill, liberty and choice are moral and political
notions that cannot be negotiated away with percentage votes.  In preserving the right
to liberty, Mill speaks for a notion that is absolute, a condition or reality that is
absolute.  In his commitment to freedom and choice, one understands that Mill's
insistence is motivated by the belief that liberal democracy exists with compromise, but
there are some conditions and realities that are transcendent, incapable of compromise. 
Freedom of thought and expression are such conditions.