Combined, perhaps, with a commitment to the protection of civil liberties for all people (gay marriage is a good current barometer of this).
I don't know if legalization of gay marriage is a good barometer of this. I read an article somewhere (I forget where) to the effect that it may not be. The reasoning went that gay marriage issue is sort of a perfect storm of hot-button issues for people. There is currently heavy investment in PR efforts and grass-roots networking efforts which may be helping to (for now at least) keep people from flipping on this issue... but only on this issue in particular... when you look at states with elected officials who are out, you see a different story -- one of increasing acceptance. So, a better barometer might be the ratio of out officials to state population. At least with this barometer, you have more data to work with, although there still isn't much.
This map shows the number of out officials in each state:
http://www.glli.org/out_officialsThis page gives the population of each state:
http://en.wikipedia.org/wiki/List_of_U.S._states_and_territories_by_populationI ran some of the data into a spreadsheet, and this is what I got:
state / number of out officials / total population (2008) / ratio (times 100,000)
OR 14 3790060 0.369387
WA 35 6549224 0.534414
CA 160 36756666 0.435295
RH 6 1050788 0.571000
FL 28 18328340 0.152769
TX 20 24326974 0.082213
PN 51 12448279 0.409695
NY 46 19490297 0.236015
MA 30 6497967 0.461683
CO 11 4939456 0.222697
DC 66 591833 11.151795
NC 9 9222414 0.097588
DE 6 873092 0.687213
Of course, this is just data, and there is always a more complicated story behind the data. DC is obviously a pretty weird place due to all of the government employment there. The quality of life in DC isn't two orders of magnitude better than anywhere else... As of the early 2000's, 4 out of 5 high school students in DC score more than 200 points below the national average on their SATs. 100,000 people in DC live below the poverty line... that's 1 in 6...
DC aside, I think one thing that will really drive up these numbers is relatively large urban areas... urban areas can, to a point, drive demographics to be more progressive... but with urban areas can come other social problems...
I don't think that these numbers are useful comparators when they are generally within the same order of magnitude... the difference between WA and OR for example could simply be due to urban populations... get into rural OR and rural WA and you might find essentially the same attitudes... Maybe OR has a larger ratio of rural to urban population, thereby driving OR's number down? Certainly, whatever the case is, it doesn't portend well (relatively speaking, anyway.. have a look at texas or NC...) for OR's statewide policy, but the urban areas in OR and WA might be quite similar to one another? Might not be? I dunno. I haven't been up there much.
NC and TX are the lowest in my list here, but they aren't that terribly far off...
I guess to really try to make any sense out of this paucity of data, you'd have to figure out standard deviations and such, to try to figure out what's significant, and by how much. You'd totally have to write DC off as a special cause variation and not include it in the standard deviation calculation.
I don't really have the firepower or the affection for numbers to do much with this stuff, however. As it is I crashed firefox trying to cut 'n paste the spreadsheet results.