An equalizer is something that gives people the same amount of power or status. "Math is the great equalizer", said Jaime Escalente in "Stand and Deliver". Education helps enormously to reduce the difference between the upper and lower classes (see upward mobility). A gun is also an "equalizer", as it enables a weak person to defend himself from a stronger, faster aggressor.
Liberals often say they want equality, but actually they have pressed for gun control laws that make self-defense difficult for the people who need it the most: urban inner-city blacks. They also have gained control of most states' public schools and are teaching math (and English) in such a way that by the time schoolchildren are ready to graduate high school and become adults they cannot use math well in everyday life.
Democracy is another example of an equalizer: everyone has an equal share in power, so that those who are disadvantaged have the opportunity to use their vote and their voice to win equality.