Is Sexual Reproduction Important?

I read a part of the book Sex Advice for All Creations by Dr. Tatiana's which compared how asexual organisms and other organism reproduced, and how certain ways of reproduction affected the genetics of organisms. As I read this section, I was posed the question "Is sex important?" At the end of the selective reading, I believe that sex is important for several reasons.
One, asexual species usually become extinct pretty quickly. This causes "scientists to conclude that exclusive asexuality is an evolutionary dead end, a fast track to extinction. Sex, they insist, is essential" (216). There are several reasons for this which will be explored later. In short, without sex, or the mixing of genes, species usually become extinct.
Two, sex mixes the genetic information from one female and one male, which helps prevent diseases and viruses to spread to offsprings. Dr. Tatiana points out "Sex is an advantage because it breaks up gene combination nations: it creates the genetic version of a moving target. With each act of sex, the parasites have to start again from square one" (228-229). If organisms reproduce without sex, which is done by cloning, their genetic information barely changes, only slight changes are caused by mutation, leaving the disease or viruses being able to evolve and maybe cause an extinction of the species
Three, according to the ratchet theory, "asexuals are evolutionary short-lived because, over time, the number of harmful mutations they carry will irrevocably and inevitably ratchet upward" (226). The ratchet theory explains that without the mixing of genes, or sex, will cause the number of harmful mutations to go up each generation of the species, eventually causing them to go extinct.
Finally, sex keeps the whole of the species more healthy than asexual species. This is because "Shuffling genes can help us evade parasites and reduce the impact of harmful mutations" (231). To conclude, even though some species can survive without sex and clone themselves instead, sex shuffles genes, causing the risk of harmful mutations, diseases, and viruses to go down, while asexual organisms have no way to stop harmful mutations to be passed on to the next generation and stop disease and viruses from evolving.
Nothing really confused me in the reading, but one question did come up though, what does celibate mean? I wish to learn about the hormones that cause the need for sex, why some people prefer certain genders over others, and what causes these preferences.