This post is partially inspired by Jonathan Miles' comments regarding the last Moose and Dude comic. However, I felt that it was too off-topic to continue in that thread and I hope it will warrant discussion on its own here.
Jonathan mentioned, and Arthur continued to discuss, the fact that certain aspects of Jonathan's argument hinge on empirical data. In particular, in order to measure the force of Jonathan's argument, one would, minimally, need to determine what, if any, connection exists between beastiality and the "slippery slope" of harm. This brought to mind a particular concern of mine in ethics. Presumably, one probable avenue for attempting to determine whether any such connection exists would be the use of statistical analysis. For example, one might attempt to discover a significant correlation between people who engage in beastiality and people who engage in particular harmful behaviours.* This, it seems, is a fairly popular way of doing things. For example, I'm sure many of us have seen the commercials that tell us that if we eat dinner with our children, they are less likely to drink or do drugs. Presumably, this statment is based on some statistics about families eating dinner together and underaged drinking and drug-use.
I have always found such statements extremely troubling, mostly because it seems to me that saying "There is a statistically significant correlation between X and Y" is NOT justification for saying "X makes Y more likely." Largely, this is because there are other factors that might be involved. In the case above, for instance, it has always seemed likely to me that a correlation in that case indicates, not that eating dinner with one's children will keep them out of trouble, but that many parents who are able to keep their children out of trouble through good parenting also eat dinner with them. Thus, if you are a terrible parent, you should not conclude (as the commercial seems to indicate) that if you start eating dinner with your child every night they will begin behaving well.
It seems to me that such cases are particularly problematic in the sort of psychological/ethical cases we are discussing here. If we were to discover a correlation between beastiality and harmful acts, would this really indicate that beastiality leads to such things? It seems to me just ask likely that the stigmatization of beastiality in our culture might make it such that only those who are otherwise troubled psychologically would engage in the activity. (Please note that these are just possibilities, I am not asserting any of this to be the case.) If this were, indeed, the case, then one might find that were beastiality not stigmatized, such a correlation would no longer exist.
Anyway, I think I've said enough here, and I'm quite interested to hear what others think about this issue. In particular, aside from comments about my reasoning, I am curious what alternatives others might offer for discovering the answers to empirical questions such as those raised by Jonathan's argument, assuming they share my worries about statistics.
PLEASE understand that I know little to nothing about statistical analysis, and it may very well be the case that I missed something, or (perhaps the more likely case) that this is an issue that has been discussed and dealt with many times and it just happens to be that anti-drug groups don't bother to worry too much about truth in advertising.
*I say "particular" because showing that someone has sex with sheep and is mean to their brother--or engages in any number of other harmful activities--probably wouldn't tell us much, as many people who are mean to their brothers don't have sex with sheep. I have in mind here specific types of harms, most likely serious crimes, that could be shown to have a particular connection with beastiality.