What consenting adults want to do should be their own business, as long as they are not harming or likely to harm someone else. That's what freedom is. And I mean directly harming, none of that slippery slope indirect nonsense. What I have a problem with is people wanting to be able to do something and force everyone to accept them with their choice lifestyle (i.e. force their beliefs onto others). Let's take gay marriage as an example. A gay couple wants to get married. Fine, but if a Christian minister doesn't want to marry them, he shouldn't risk being sued for that.
On another note, restrictive laws (on consenting adults) seem to be some of the most contradictory laws in existence. There is really no correlation between what an adult legally can and cannot do. Note some of the following (going by US/California laws):
An adult may purchase and smoke tobacco/cigarettes, which are addictive and toxic.
An adult may not legally purchase or smoke marijuana, which is virtually non-toxic, non-addictive, and has many medical and non-medical uses.
An 18 year old may own a gun. An 18 year old can get married. An 18 year old can vote. An 18 year old can go to war.
An 18 year old cannot purchase or consume alcohol (which means one cannot drink at one's own wedding or perhaps at as a celebration after returning from deployment as a veteran).
An adult may gamble in a casino or play the lottery. An adult can buy stocks, invest money, borrow money, or give away money. An adult can be sued.
Online poker/gambling is, however, illegal in the United States (not entirely sure on the legality, but all online poker companies refuse service to US customers claiming restriction by the SAFE Act of 2006).
An adult may act in pornography.
However, prostitution is illegal. I guess it's okay to be paid for sex if there's a camera involved?