The "police power" is the government's power over matters affecting the healthy, safety, and welfare of its citizens. In the United States, only the individual states have the full police power; the United States' police power is limited to matters of federal concern (e.g. crime on federal property or violation of a federal law that is based on a constitutional power).
The police power is often used to prohibit behaviors whose primary fault is that they're immoral. (Presumably, immoral in the opinion of the legislative majority.) This is most obviously true for laws prohibiting prostitution and regulating alcohol and sex-oriented businesses, but it's also true for laws forbidding gay adoption and car sales on Sundays.
Use of the police power to forbid immoral acts that are not otherwise harmful to life or property is justified on a collateral basis. That is, prostitution spreads STDs, drugs promote property crime, and so forth.
An approach to governance strictly designed to maximize personal freedom (e.g., some forms of libertarianism) would oppose the use of the police power to forbid immoral behavior.
So, is the prohibition of immoral behavior reasonable on the grounds that you're actually preventing collateral harm? Let's look at Nevada. Nevada has legal prostitution, legal gambling, and cheap booze, all generally prohibited as "immoral" by other states. In addition, Nevada's history of easy divorce is also generally considered immoral, even though it's been duplicated by most everyone else. If the immorality theory holds, Nevada should have noticeably more crime than other states.
(Nevada crime statistics) In 1997, Nevada is ranked 35th in population, and per capita is ranked for crime:
OK, gee, it sure sounds like there might be something to this "immorality" thing. Nevada citizens have to put up with a whole lot of crime, it seems. They're at or above the median (25th rank) for everything except basic theft.
Refinements to the crime stats: Nevada has a lot of tourism--all those people flying in to do immoral things--so maybe that brings the numbers back in line.
Las Vegas had a population of about 478,000 in the 2000 census (cite). (Tourism stats) Las Vegas has about 105,000 hotel rooms, which are 86.4% full at any given time, adding about 91,000 transients to the city's population, a 20% increase. Las Vegas, of course, is going to have a plurality if not an absolute majority of Nevada's tourist population.
For comparison, Utah, the 34th most populous state, has about 200,000 more people than Nevada; Nevada's tourist population is going to bring it in line with Utah in terms of population. Does that spread the crime out enough to lower its ratings significantly? No. The difference between Nevada's 14th rank in burglary (877.1/100,000) and Utah's 27th (642.5/100,000) is far more than could be explained just by increasing the denominator in the per capita rate, for example.
Utah is a good comparison, because Utah is a restrictive state where Nevada is permissive (no whoring or gambling, and limited alcohol), and they are geographically proximate. As noted, Utah is 34th in population, and per capita crime works out to (cite):
Those statistics are remarkably different from Nevada's. Nevada's crime rates are generally high almost across the board, whereas Utah is either low or high. In Utah, you're not going to get murdered or beaten up, but you will be robbed or raped. Odd. And, in fact, there's enough theft in Utah that the total crime index is actually higher than Nevada's.
I won't repeat the full list, but in Massachusetts, a notoriously liberal (= immoral) state, crime is low, and the only thing you're at risk above the median for is getting beaten up or having your car stolen.
So, I'm going to say that, based on a couple minutes' research, the data isn't especially clear. There does appear to be some spillover from immorality into serious crime in Nevada, but prohibiting immorality doesn't appear to insulate you from crime in general. More study is needed.
OK, so what does this have to do with anything?
One argument against gay marriage is that being gay is immoral and hence subject to police power prohibition. As noted, the idea that the police power can encompass simply immoral acts is not a-priori nonsense. However, note that this argument, in fact, relies on an inference from an inference (in my native jargon, an epsilon-squared term). That is, gay marriage legitimizes immorality and immorality leads to actual harm. Of course, it seems fairly clear that nearly the same amount of immorality (i.e. being gay) is going to occur with or without gay marriage. Furthermore, one can argue that, even if being gay is immoral (which it isn't), the moral effects of marriage, the stabilizing effect that justifies the state's sanction, that do not accrue without state sanction, will ameliorate or eliminate the effects of the immorality associated with being gay.
Do you have access to a by-county breakdown for Nevada? Prostitution is illegal in Clark County, NV, which is home to 70% of the population.
Las Vegas is Clark County, I believe. I'm pretty sure there's a ring of whorehouses at the county line.
You can tell the difference between me and a real researcher because I'm too lazy to figure out how Las Vegas can have a population of half a mil and Clark Country 1.4 mil and how much of a difference that makes in the tourist-based de-facto population increase.
No convenient whorehouses on the strip may explain why the rape stats are so high. You get all worked up, and the whores are too long a cab ride away. <--Note to future biographers: Any reference to "whorehouses" is to be taken as indicative of tongue-in-cheek, because negative connotations blah blah blah.
Actually, just to make it more complicated:
Las Vegas is the seat of Clark County. Old Vegas (Binion's Horseshoe, etc.) is in fact in Clark County. However, the Strip is not in Clark County, but rather in a bordering unincorporated area which if memory serves is larger than the state of New Jersey.
Ed, are you sure? Unincorporated traditionally means it's part of the county but not in any municipality. This can't happen in NJ or CT (where the municipalities are wall-to-wall, like a bad shag carpet, but does happen in TX.
You're right. I fucked that up nicely.
The Vegas strip is not in fact in Las Vegas, but rather in an unincorporated area of Clark County. I read the fact a few years ago (during my last trip to Las Vegas) and promptly mangled it.