Ethnicity -- while I see no difference between the races, I've always made my sims white. Previously, I didn't think the colors given were accurate of the people I knew of other races. With Sims 3, I was able to have a little more diversity, but I still kept to the light through tan spectrum. I have no adversity to the other races already in game, but I haven't had sims marry them. In fact, there are very few townies that my sims marry anyways (I could name them on one hand), as I usually make families and don't play past 2 generations. Usually.
Sexuality -- I've only ever made two non-heterosexual couples, one for sims 1, one for sims 2. They've always been female couples and it was to see what options they had (basically no different from normal couples, aside from the reproducing matter). I was glad to see the differences were basically nill, but I like balance. I like a male and female couple, partially because that's the environment that I came from -- I didn't know of any same-sex couples until I was over 18.
My heterosexual couples are almost always families, or at least they are stories that lead to families. I can't even say that I always have males propose, because I like to preserve the family name that I picked. However, my heirs are almost always females (on those rare times that I play legacies). I'm pretty picky about how my males look, and I go for genetic potential.
Religion -- Do not care. I have previously had some non-Christian CC or mods in earlier games, but I found it pointless and do not need it in my games. I've put up the Christmas tree occasionally for the easter eggs (um...sims 1 I think it was). I am not a god; my sims are virtual pets, but I do not see them as my minions, subjects, etc. Life and death are creation and deletion of computer code or an integral part of a story for passing on the ruler of the house/town. My sims follow no path (minus the previous mention of CC/mods).
Interesting thread. I mainly don't add my own ideas into the sims themselves, but rather the houses. My houses have stories and they usually have to do with an undead legacy. Or just haunted houses in general. But I do feel bad about killing sims, which is usually why I rarely get to the 3rd generation. There was once a time where I did kill sims on purpose, but that was to make tombstones that had ghosts. To freak out the residents of course >:)
