i have no doubt that this happens, happens a lot, and that it is frustrating. there are difficult currents at play in the discussion of any heavily loaded subject. however, "other views" does by no means equate to "opposing views"; casting the conversation immediately as controversial is not productive. furthermore, throwing in a historical example of people who might've felt similar to you isn't a change of subject in and of itself; who says you have to go down the path just because a gate has been opened? and railing against something that is a normal and deeply engrained part of how people communicate in this society (offering their own experience/knowledge), is like fighting with windmills. telling everyone of race X to shut up is bordering on racism itself; it certainly shows that one has strong stereotypes. i can guarantee you it won't lead to people of colour feeling heard. instead it'll lead to further alienation of people who're actually allies.

there are ways around feeling that one's not heard which are IMO more useful. one is to restrict the audience, and to set rules of order (possibly using a facilitator if the discussion needs to happen at a level above the watercooler). another is to not let somebody else's experience take over the conversation, but to either acknowledge it ("yes, that's true about the irish") and walk past that opening ("but i don't want to discuss the issue of racism in a historical context right now") or refocus ("but i want to just talk about my personal experience right now"), or use it to underline and contrast one's own experience. one can also ask the individual whose contributions grate to please just listen for the time being (and then give them the floor when you're done, or at another set time). oh, and if it happens in one's LJ, ban shit stirrers and trolls without making a fuss about it (the fuss and general engagement with such people is what really derails the conversation).