The Left: For the greater good, restrict economic activity & redistribute wealth to promote equality of economic outcomes The Right: For the greater good, restrict sexual activity & impose early, lifelong monogamy to promote equality of mating outcomes Libertarians: Freedom.
'Early' = discourage premarital sex. 'Restrict' = outlaw any form of marriage other than monogamy. 'Impose' = give tax incentives for monogamous marriage.