My own experience as a southpaw in a right-handed world hasn't been much more than an annoyance, much like having to adjust one's pants constantly because they don't fit right. I'm white, male, and heterosexual: I don't know what real oppression feels like. Being left-handed means I have experienced just a very small taste of what it's like to be different - what being a minority feels like. I have felt that a little more since accepting the atheist label. If people didn't think I was in league with the devil for being a southpaw, I'm sure some of them think so now.
I have tried in the last two years or so to sensitize myself toward issues which have never and can never affect me directly: issues pertaining to women, homosexuals, and racial minorities in particular. I can't say I have it all figured out yet. My difficulty is based on the fact that I have no existential knowledge of what discrimination feels like. Sure, I have tattoos, and I'm an atheist. Like I said, I have experienced a tiny amount of discrimination. I know atheists who have dealt with much worse than I have; nevertheless, prejudice against atheists is still alive and well. Has our society reached the level of tolerance and understanding and acceptance towards atheists? Not even close. We have a black president (which is an incredible victory, and a major moment in history). I doubt we'll see an atheist president in my lifetime.
I'm not trying to draw comparisons here. It's silly to try to determine which group deals with more prejudice, or even to compare groups at all. I don't think atheists have it as bad as other groups. It doesn't really matter which group is discriminated against more. The fact that there are bigots in the world who have made life difficult for people because they're "different" should be enough to motivate us to take a stand for justice, tolerance, fairness and equality - aequitas - for all people, regardless of gender, race, religion, age, disability, body type, sexual orientation, tax bracket, or lifestyle. I can't understand what it's like to be gay, or black, or a woman. I won't be so arrogant as to assume that I can understand the effects of bigotry, or what it feels like personally. All I can do is show my support, and learn as much as I can.