In the posts on this topic that have been appearing on my friendlist, the irritation is because the topic invariably turns away from minorities' current experience of disenfranchisement and prejudice in the U.S. to either a historical perspective with the various European immigrant groups, or the current disenfranchisement/prejudice of various groups of whatever hue in other countries. I'm pretty sure this is because everyone wants to bring their own personal experience to the table, and when you're a member of majority culture, your personal experience is naturally going to be different, based in a different historical or social context than that of the people who initiated the conversation.

Basically, the poeple I've been reading are trying to focus the conversation on one section of the topic that they feel doesn't get enough attention, and the people they're irritated with keep coming in and sidetracking the conversation, and they're seeing that it pretty much divides neatly down minority/majority lines.