Liberals believe in equal opportunity.
We would not have fair employment and fair housing laws without liberals in government pushing for rules that discourage discrimination based on race, religion, gender. Some of the big impact in governance through liberal philosophy have been the rules that protect opportunity and the right to vote.
It is one of the finest qualities in liberal philosophy. Conservatives try to turn this positive into a negative by complaining about political correctness, impositions to the existing (stratified) social order. They even claim we are trying to guarantee equal outcomes beyond the concepts of equal opportunity. We need to remember that freedom and political power for all were enshrined in laws by liberals to protect from discrimination based on race, religion and gender.
Soon we may add orientation the that list. It was impossible for the slavers of the 19th century to see the wisdom of the abolitionists. Men in power could not hold back the tide of a generation of women pushing for suffrage. Each of the turns of the struggles for greater equality among the people has only marked the beginning of larger shifts toward freedom within our culture. There have been long drawn conflicts over how to approach the matters of equality but liberals have always been on the side of equality and freedom for all the People.