...that knowing too much about some actors' personal lives may color our perceptions as well. As you described below, some actors are adept at playing a range of characters and some are not, just as some are facile with accents and mannerisms and some are not. But sometimes, we as an audience add an additional layer because of what we know or have seen of their personal or public persona.
In the end, sometimes casting works and sometimes it does not.
For me, I have found in my professional life that people's sexuality is much more fluid and complex than could ever be neatly categorized into a simple dichotomy of straight vs. gay. Hence, I would be willing to give nearly anyone a chance to play any sexuality. This is not the same as race or ethnicity or even gender.