The many sexual issues include the topics of homosexuality, prostitution, extra martial affairs, contraception and sex before marriage, with many of the theories giving their view on what is right or wrong. Aquinas theory of natural law is one that says no to mostly all sexual issues. He thought that sex had three purposes, to reproduce, provide pleasure and to bind a husband and wife together. So with that he completely argues against the use of contraception and also homosexuality. Aquinas said sex is used for procreation so using contraception to stop it is wrong as it goes against the natural order of things. Similarly with same sex marriages, being gay is not wrong but acting on it is as there is no potential to reproduce.
Natural laws belief of sexual issues could be argued to be an effective theory to make sexual decisions. It gives you clear rules on what is right or wrong and there is no room for interpretation. Meaning that the theory is easy to follow and treats everybody as equal, everyone knows what the right thing to do in a situation is. However it is an idea that is very outdated. As culture changes so do the views and attitudes of people. So in times today homosexually and the use of contraception is alot more acceptable and happens more often. Aquinas' ideas are no longer a strict set of rules people feel they have to follow so in more modern days it is not seen as useful.
Utilitarian's take a more pleasure seeking approach to sexual issues; they are drawn towards pleasure seeking and reducing pain. They would say that extra marital affairs are acceptable, but only on the condition that both partners are consenting and it is the most pleasurable for the most number of people. However they then would consider the long term happiness, will what is pleasurable in the short term be so in the long term too. Utilitarian's would also accept