We need to legalize polygamy. Our society would benefit from the stability that plural marriages would provide. There is no good reason that polygamy is illegal.
I'm not talking about a stagnant gene pool of polygamists living in an isolated religious community, I'm talking about a general acceptance of the plural marriage concept; no religious strings attached. Women should be able to have more than one husband, and men more than one wife.
Consider the implications of polygamy in western society. Wealthy and successful people could create legally binding, stable relationships with numerous mates of their choice. The gene pool would be improved because superior genes would be replicated at a higher rate. People would be able to optimize the viability of their offspring without resorting to genetic engineering. There would immediately be fewer unmarried women, which would force men to be more attractive on all levels, which would drive our species to higher levels. The same would be true for women. Basically, evolution would ramp up at a higher rate.
Legalized polygamy, coupled with legalized prostitution, would provide our culture the necessary vehicle for a more natural sexual environment.