Earlier quoted context omitted.
If people consider marriage as a contract of exchange, then it is already a form of legalized prostitution. Monogamy might be a bigger underlying problem. Esther Perel's Mating in Captivity in a good read on this topic.
People who think like this don't tend to stay married long.
I started out married thinking of it as a nebulous thing. My marriage improved when I realized it was all an exchange and I need to make sure I'm always providing my bit rather than just working towards some nebulous idea of love.