. . . I admit to have taken advantage of mistake fares in the past such as expedia.com.br (although that was more a loophole than a mistake) and one ex-RGN fare. Also had several cancelled without a whisper of a protest from me (easy come ... easy go).
However, I do believe it is wrong to whinge, and pursue legal action when the mistake fare tickets are cancelled by the airlines ... if you followed the RGN fiasco a few years ago of flyertalk, it was quite breathtaking and IMHO so wrong on many levels, the lengths people were going to, to challenge airlines regarding re-instatement of so obviously mistake fares airlines had cancelled (with the exception of those cancelled on day of travel .. if booking made months in advance, and it is a mistake, fix it before the traveller gets to the airport).