Moving beyond the fact that the first paragraph seems to imply that the tumblr is about you. The question is an interesting one, the impression I got from the tumblr was more about social trends and prevalent ideas than it was problematic individuals. As a poster above points out, were it to be about that, the contact details of the people in question could be given out.
If I formed part of a trend of misogyny and racism, then I would see no wrong in being labelled as such. If I am putting myself out there in a public forum with such views (I have no problem putting my own face to my posts here for example, see that guy to the left of my post, that is me) then I should be capable of dealing with the consequences when the response is within reason. If, in some GAF meta thread, someone took a bunch of my posts and, say, got me to argue with myself, then I might be a little hurt, but it would be only my pride. I would be wrong to respond to it with offence, simply because I should not get upset about my own views, my own inconsistencies. If you feel that I am a hypocrite, you are welcome to take my photo and do exactly that. Even make a OS tumblr if you want
As the tumblr does not post pictures of these men with captions that imply any more than what they have said themselves, I don't see the problem with it. These pictures are accompanied with their real opinions, if it were 'I like to murder people' on a picture of someone that had no homicidal inclinations, then it would be a different matter.
As I said, it relates to social trends, rather than individuals.
I concur on the moral problem with backbiting. However I do not think that this necessarily falls under that umbrella.
In general, the main form that the tumblr takes is of juxtaposing the assertions of individuals with their own perception of themselves as 'nice guys'. I do not think that this is any great moral wrong. It is a situation where one must weigh up possible harm (people getting their feelings hurt) with possible benefit (problematic trends highlighted and critiqued).
Considering the subject matter of some (rape, eugenics etc.) the possibility of people getting their feelings hurt for holding offensive views comes off second to the importance of highlighting the problems with said views.