A new study, "Should Mary and Jane Be Legal?," in Public Opinion Quarterly traces the changes in American attitudes toward both legalization of marijuana and same-sex marriage from 1988 to 2014. The Indiana University researchers use data from the General Social Survey to see how views changed over time. The researchers point out, "Because support for marijuana and same-sex marriage legalization have not been explicitly compared, we do not know exactly how attitudes toward these issues have moved together over time, whether people who support marijuana are the same people who support marriage, nor what might predict someone supporting one issue but not the other." So they compared four groups of people: (1) those who support neither; (2) those who support marijuana but not same-sex marriage legalization; (3) those who support marriage but not marijuana legalization; and (4) those who support both.
They found that …
…support for marijuana legalization more than doubled from 1988 (17.7 percent) to 2006 (38.4 percent). Support for same-sex marriage legalization almost tripled from 1988 (12.1 percent) to 2006 (35.6 percent). In 2012, slightly more than half of all Americans supported marijuana legalization (50.3 percent) and same-sex marriage legalization (50.6 percent). By 2014, almost three out of every five Americans supported marijuana legalization (57.4 percent) and marriage legalization (57.8 percent).
Basically, support for both the legalization of marijuana and same-sex marriage increased as opposition to both fell. In other words, over the last three decades Americans have been adopting a more libertarian attitude toward both.
The researchers speculate:
Why are seemingly disparate issues evoking similar ideological responses? Both marijuana and same-sex marriage legalization are related to individual liberty and what the government should and should not regulate, and therefore our findings may reflect a broader shift in the public's support for maximizing individual freedom—or autonomy—and not regulating behavior that does not affect others. Our findings speak to the possibility of a wider liberalization (or maybe just libertarianization) of American attitudes that should be examined in future research.
In 1988, most Americans wanted the government to regulate these issues, but in 2014 Americans want people to be able to choose for themselves whether these behaviors are right for them. … Policy legitimation justify and reinforce the redefinition of marijuana and same-sex marriage from behaviors to regulate to issues of individual autonomy that, in the views of many, do not have much effect beyond the individual.
I think that their findings do reflect a broadening of public support for maximizing individual freedom.