I know that "man's anger does not produce the righteousness that God desires". But I also know from Jesus' example that there is such a thing as valid, righteous anger. The danger is that when I feel a desire to be unreasonably angry, which is fairly often, I try to find a way to classify it as "righteous anger" so I have permission, or even an obligation, to let that feeling flourish. Better still if some other person validates my anger, commends it, or commands it as a duty! Often the Internet is an excellent resource for finding validation for my anger.
This is especially pernicious when the permission is actually reasonable but I use it as an excuse to enjoy rage. It's easy to look at the world and feel justified anger at, say, the latest irresponsible behavior of technology vendors. But since there's little I can do about it, feeding such anger is counterproductive; it makes me an angry, grumpy, frustrated person with an inflated sense of superiority and scorn.
A completely different sort of example is racism. Some forms of racism come easily to me and I have to be constantly vigilant against them. If someone (not naming names, cough cough) or some community was telling me it's OK to be racist (explicitly or implicitly), my job would be that much harder. Although there isn't any sort of "righteous racism", there are justified complaints about aspects of specific cultures that can be used as a cover for racist feelings. To dodge this problem, many communities try to exterminate the permission by treating any criticism of culture (or at least certain cultures) as de facto racist; this goes too far. I just try to avoid thinking about these issues unless it's really necessary, which it seldom is, and when I do think about them I have to be very very careful.
I think everyone needs to learn to identify those moments when we're seeking permission to indulge a sinful desire, and understand that even valid grounds for that permission does not validate the desire.