(July 9, 2015 at 7:55 pm)Mr.wizard Wrote: I don't understand the std argument, If everyone in a polygamous relationship is faithful, your not any greater risk. Its exactly the same for a monogamous marriage. I don't have any moral objections to polygamy assuming all parties are consenting, I think the problems are with child custody and division of assets.
Yes, IF everyone is faithful, then no STDs will be added to the group (let us ignore things like sharing needles that can also get one STDs). However, in the real world, some people cheat, and some do not. The larger the group of people you collect together, the more likely there will be at least one of them who will cheat.
Now, it may be that with your large group, you will be very, very lucky and no one will cheat. But cheating is a common problem, so that one should expect that someone probably will cheat if there is a large group of people involved.
We can try to approach this from another angle. We can divide everyone in the world between those who would cheat, and those who would not cheat. This is an abstract division, and we are not going to be able to tell by looking at them which ones are the cheaters and which are not. It isn't as if cheaters had "CHEATER" tattooed on their foreheads.
So, if we select two of the people, it might be that we have not selected any of the cheaters in the world. If that is the case, and they do not add anyone to their group, then they don't add STDs to their group. But, if they add a person from the world to the group, it may be that that third person is a cheater, and if that is the case, then they may add STDs to the group. The odds are greater than zero (that is to say, it is possible) that the third person is a cheater, and so they increase the likelihood of getting STDs by adding that third person to the group. The same idea applies to adding additional people, with each new addition.
Of course, if the first two already involves a cheater, then they already have a chance of adding STDs to the group. But we do not know that one of the first two is a cheater; they may or may not be. That is, there is a chance that neither is a cheater.
With each individual person, there is a chance that the person is a cheater, and there is a chance that the person is not a cheater. The more people you select, the more likely it is that at least one of them is a cheater.
"A wise man ... proportions his belief to the evidence."
— David Hume, An Enquiry Concerning Human Understanding, Section X, Part I.
