I was just looking at the Pew survey data linked above. It's striking that the views of Americans on abortion are mostly split along lines of religion, political inclination and education. Factors such as age or gender don't really matter that much. There appears to be some effect of race, with Hispanics being less likely to be pro-choice than black or white people. I would like to think that this could be an effect of religion disguised as a racial or cultural difference, but I assume that Pew controlled for that in their reported data. To summarise, the results suggest: The more dogmatically religious you are, the more likely it is that you will think that abortion should be illegal. Conversely, the more relaxed you are about religion, the more likely you are to be pro-choice. Conservative Republicans are a lot more likely to believe that abortion should be illegal than liberal Democrats, and vice versa for the pro-choice position. The higher your level of education, the more likely you are to be pro-choice. It is interesting to speculate on what the "main" factor at play might be here, if we were to try to reduce it to one (which may or may not be possible). I would tentatively suggest that the determining characteristic is a person's conservatism vs liberal outlook. It seems to me, as an outside observer, that if you hold conservative views you're (a) more likely to be religious, (b) more likely to vote Republican than Democrat, and (c) less likely to have a college (liberal arts) education. I also find it fascinating to think about causation on this. For example, perhaps religion makes a person more conservative, which means they are more likely to vote Republican and less likely to think outside the box. Or maybe being exposed to Republican views, at the expense of Democrat ones, makes a person more conservative and hence more likely to become (or stay) religious. Or maybe having a low level of education makes it more likely that a person will be persuaded by the arguments of religion and/or Republicans. It's complicated.