Groan.
First, I don’t regard anyone here as a PC poopiehead–but I do think that that’s the level of dicussion going on here. I love our language and it’s complexities–I wish I knew more about entymology (sp?) and linguistics. you with the face said that '“White” in the noble sense is not a common feature of the modern American vernacular." and perhaps that is true. What might be most precise is that I am not a common feature of the modern American vernacular. Let me explain what I mean.
If I were to have to quantify the degrees of racial epithet to sardonic commentary for this phrase, I would have put it at about 2% racial and 98% caustic deriding. Add to the fact that I now know some black folks (my friend’s parents) who have apparently used it and that we joke around at work with it(I am one of two white nurses, the rest are black or Asian)–I am amazed and appalled at the interp being made here.
I would think that instead of posters claiming loud and long that it could ONLY have racially charged meaning, that they in turn would consider that the phrase might have more than one intent. But no, that has not happened. It must be and only is racially reactionary. I disagree.
Add to this also that I am a demon for reading British lit of almost any era (I draw the line at Chaucer-who wants to work that hard?), and that my sister has a degree in medieval studies, my parents are European history buffs, and my sons are obsessed with castles, battles and knights etc–clearly I am NOT a “typical” American (whatever the hell that may be). Did you know that England used to be Albion–from Alba. Gues what alba means–it means white. Gah! the whole island is racist! 
None of this is important to the generalities of life. One should not have to explain one’s background in order to be understood! I am not suggesting that by any means. But to say that I was being wide-eyed and “pretending” not to know about the dirty underbelly of this phrase is just plain wrong. I assumed that Dopers would read my post (complete with clarification) and understand the intent of my remarks to poor Martin.
I was aware of of the nastier interpretation. I thought (how silly of me) that since it has more than one meaning(with the racial one being secondary), my intended meaning would stand. For some, it did not–in fact, that meaning is dismissed outright. That I find disingenous and offensive. If you want to claim Doper status, you had better be prepared to have your ironclad assumptions about Life and Important Things challenged. Some things are more than you suppose–some things much less so. C’est la vie.
I see here a sort of group hysteria surrounding the use of an idiom. asterion has some excellent points. I appreciate that post. I won’t go all grand and highfallutin’ and cry, “Save our noble tongue!”, but I am irked that something as simple as this–which, for the last time, no-one is using as a compliment, should put so many up in arms.
Zoe -I thank you for the nice things in your post. I see your point. I tend to believe that bit about messages perceived and messages sent etc as well. But this feels different to me. A misperception would have been cleared up long before now. Not only that, but there should have been no misperception in the first place, as my usage was clearly delineated. God knows I am enough of a pragmatist to usually shrug stuff like this off and say, ok, folks-got it and move on.
But I won’t. There is something else going on here-I am not sure what, but this is more than a discussion about a turn of phrase. Somehow, this either frightens people or threatens them in some way–or there are alot of Dopers who need busier lives! 
In a strange way, I feel like we are talking about something else under the guise of complaining and defending the use of idioms. Or maybe that’s my cold medicine doing my thinking for me.
I suppose I will open the gates of Hell here if I liken the use of the phrase to the use of the word “niggah” or “nigger” by the black community in reference to itself. Being white, I don’t know a whole lot about that, but I do know that it is quite controversial and can be inflammatory. Oprah did a show on it–I believe she took Chris Rock to task about his using it. Apparently, some younger blacks are using it (to what purpose I know not, except in Rock’s case, to be funny) and this has appalled some older folks.
God, I just see this being misconstrued into me wanting the word “nigger” to make a comeback. Nothing could be further than the truth. Just as I do not desire (and would not use) the phrase, “mighty white of you” IF the white supremicists and prejudiced morons reclaimed it for their own. I dont’ see that happening.
If anything, from where I sit, I see the phrase taking on new, better life–one that deprecates the receipient in such a way as to expose hypocrsiy and pomposity, one that mocks the very core of racism that it apparently sprang from.
Frankly, I can’t see how ANYONE could look at it and think that the deliverer is touting white superiority in any way. To me, that says that 1. you don’t understand satire, 2. you don’t understand language and 3. that you feel threatened by confrontation that doesn’t involve name calling and swear words.
This does not imbue respect in me. Perhaps if I had just called Martin a dickhead, we would all be happy now. Well, I wouldn’t be–dickhead is a stupid, sophomoric name to call anyone. Not only that, I was criticising his actions–not his person. There’s plenty of the latter(too much) online and here.
My mistake (if it can be called that) was to expect a level of sophistication and insight on the part of other Dopers. Apparently I missed that mark.
askeptic --if what you have posted is true, why did you ask me “what the fuck does that mean?” in the other thread? Why did you not then say, “hey! I’ve got a racist uncle who says that! Don’t use it.” I think that you did NOT fully read my post where I not only used the phrase, but also stipulated what I meant by it. In short, I think you started a shit storm for no good purpose.
In conclusion (how pompous of me, sorry)–I shall continue to use this phrase for several reasons. Not only for the ones I laid out above, but also for the very reason that it has caused such a brouhaha. Essentially, I will not cowtow to the PC police (here and elsewhere). I am appalled at the eviscerating of English in recent times–the psycho-feel good babble and euphemisms that make inclusion and sentiment paramount to precision and incisiveness.
Me not saying “that’s mighty white of you” doesn’t make racism go away, doesn’t rid the world of malicious remarks on unacceptable groups (the mentally ill, in case you’re confused), won’t show up the perpetuators of same for what they are. Of couse, my using the phrase isn’t likely to save the world, either, but that’s not the point.
This has been a very interesting window into different views. Again, I apolgize for any inadvertent offense I may have caused. Forgive me for being a PIA, but a careful reading of my posts would have shown everyone that such an offense was never intended.
You have every right to your feelings–I just don’t enter into them. If anything, I feel quite strongly the other way!