'Knee-jerk conservatism' is merely the proper and automatic recognition of right and wrong. All else is sophistry.
As for prostitution:
Prostitution is wrong because it spreads disease, both physical and moral.
There are many who, including those who were sex-trade workers, see prostitution as slavery.
Legitimizing the sex trade will also have the undesirable effect of making it more acceptable. Moral decay is a label that liberals usually equate with 'meaningless religious argument.' Then they stop paying attention. If you are honestly liberal in thought, you will consider this viewpoint even if it differs from yours. Sex is a part of the procreative act, designed for the perpetuation of our species. It leads to the creation of children who are best raised in a stable family environment of a Father and Mother. The most stable parenting arrangement in history is a Husband and Wife in a covenanted married relationship. It is morally repugnant for a society to encourage the destabilization of the family unit, in this case by making illicit sex licit.
Science has proved that there is no such thing as safe sex. Condoms were designed to prevent pregnancy. I remember reading reports of tests that showed the best Condoms have consistent failure rates as high as 20%. When you factor in all the various activities that can be included under the heading of 'intercourse' (Billy Clinton's bizarre definition excepted) the failure rates can approach 100%.
When you consider the incubation periods of some STDs you can see there is no such thing as a 'safe' sex-trade worker.
There is also the medical threat to the innocent. As a former reporter I've spoken with sex-trade workers, and they'll be the first to tell you a large percentage of their 'johns' are married men. The health of the wives of these married men is jeopardized by their mate's infidelity.
Government Regulation won't prevent STDs from spreading through the sex-trade either. Jurisdictions where prostitution is legal have umpteen regulations against unprotected sex. Yet I've read more than a few reports that unprotected sex is available for an extra fee in supposedly 'regulated' establishments.
It is repugnant for a pimp to benefit from the perverse thing that is the sex trade. Legalizing and taxing it merely makes the Government a pimp as well. If it is legalized, Every Government member who votes FOR this should be made to share a pooled blood transfusion from sex-trade workers.