The rub for me has never been about if healers should DPS at all but the scale of DPS that was being demanded of me even in regular roulettes. I and most healers have no issue with throwing out some damage when we feel we have the time, but a lot of time people want savage level gameplay out of healers queuing up in the DF and you probably just aren't going to get it most of the time. Also there is not content that requires healers to DPS. Unless it has changed, back in HW I think it was stated by Yoshi P that no content is designed with healer DPS taken into account. So if you are failing a DPS check or something, it is not the healers fault.