In his discussion of "cryocrastination", AndrewH makes a pretty good point. There may be some better things you can do with the money you'd spend on cryonics insurance. The sort of people who are into cryonics would probably accept that donating it to the Singularity Institute is probably, all in all, a higher utility use of however many dollars. Andrew's conclusion is that you should figure out what maximizes utility and do it, regardless of how small a contribution is involved. He's right, but I want to use the same example to push a point that is very slightly different, or maybe a little more general, or maybe the exact same one but phrased differently.
Consider an argument frequently made when politicians are discussing the budget. I frequently hear people say it would cost between ten and twenty billion dollars a year to feed all the hungry people in the world. I don't know if that's true or not, and considering the recent skepticism about aid it probably isn't, but let's say the politicians believe it. So when they look at (for example) NASA's budget of fifteen billion dollars, they say something like "It's criminal to be spending all this money on space probes and radio telescopes when it could eliminate world hunger, so let's cut NASA's budget."
You see the problem? When we cut NASA's budget, it doesn't immediately go into the "solve world hunger" fund. It goes into the rest of the budget, and probably gets divided among the Congressman Johnson Memorial Fisheries Museum and purchasing twelve-thousand-dollar staplers.
The same is true of cryocrastination. Unless you actually take that money you would have spent on cryonics and donate it to the Singularity Institute, it's going into the rest of your budget, and you'll probably spend it on coffee and plasma TVs and famous statistician trading cards and whatever else.
I find myself frequently making this error in the following way: a beggar asks me for money, and I want to give it to them on the grounds that they have activated my urge to help people. Then think to myself "I can't justify giving the money to this beggar when it would help many more people if I gave it to a responsible charity." So I say no, and forget all about it, and never give the money to anyone. Even though (from a charity point of view) I know of a superior alternative to giving the money to the beggar, I would still be better off just giving the beggar the money!
All this means that for any entity that does not use its resources with maximum efficiency, the opportunity cost of spending a certain amount of resources should not be calculated as what you'd get earn from the best possible use of those resources, but what you'll earn from the use of those resources which you expect to actually occur.
...no, I don't see why that means one shouldn't give money to beggars.
Let's say beggars in my city can make $1/hour. Everyone who, in a world without begging, would have made <$1/hour becomes a beggar, and everyone who in a world without begging would have made >$1 hour does not become a beggar.
Now let's say people in my city become more generous and give more money. The number of beggars cannot increase without the wage of beggars also increasing, because the only reason more people would become beggars is that there is a higher incentive, and if the influx of new beggars drive wages back down, those new beggars will "quit" their "job" and the hourly wage will stabilize. So it may be that now beggars earn $2/hour, and everyone who would earn <$2/hour at normal labor quits and becomes a beggar.
In a country with a minimum wage, this suggests that no one will ever leave a job for begging until a beggar's wage exceeds minimum wage; despite the horror stories I don't think this has happened here. It suggests that the population of beggars will probably consist of the people who would have a (low-paying) job if there was no minimum wage but can't get any job in the current regulatory climate. These people seem worth helping.
In a country with no minimum wage, begging establishes an effective minimum wage. That is, if beggars can earn $1/day, then no one will work for less than $1/day because they'd rather beg. This may be bad from an economic standpoint, but it's good from a humanitarian standpoint; it means we can be assured every poor person in the country will earn at least $1/day, whether working or begging, and that no one will have to make do with less. If people become more generous and donations rise to $2/day, this just means that all poor people can be assured of a little bit more money. This seems like exactly what people donating to beggars have as their goal.
Although it may leave a bad taste in our mouths that beggars are quitting their fifty-cent-a-day jobs for begging, if we place a greater value on people not having to live on fifty cents a day than we do on the "moral value of hard work", we are making people better off. We'd have to balance that against the lost productivity of these beggars' fifty-cent-a-day jobs,but if they're only earning fifty cents a day, they can't produce all that much.
[possible counter-argument: if you have a fifty-cent-a-day job, you might learn skills and get promoted. This seems a much more relevant concern in a first world country than in a third world country, where most people labor at dead-end jobs their whole lives, and since first world countries generally have minimum wages anyway, I don't consider it too important]
[this argument probably only works in Economics Land; I think gworley does a better job of describing what happens in the real world.]
I do not have hard data, but I strongly suspect a lot of beggars make more than minimum wage. Many don't, and this varies by area, but in Berkeley at least, there's a ton of foot traffic and people beg in the same spot day-in, day-out, and I would make a large wager that some if not most of them make more than $7 an hour, on average, tax-free. In fact, you occasionally hear about someone who is employed or on disability or otherwise should not be begging doing it on weekends to make a bit extra, though this is more an issue of supply size than it is of wage.