I haven't read the thesis, but my brief glance at the DM article tells me that they personally didn't advocate using child porn as harm reduction, but were talking about how others had done so in a review of the literature. If it were in their own list of recommendations that's different, but reviewing literature shouldn't be taboo.
Crime prevention have discussed things like using sex dolls as a potential harm reduction strategy, a police officer once asked me about it (I didn't know as it's not my area).
I don't think throwing stones at this person is helpful in preventing child sexual abuse at all. Demonizing and stigmatising child sex abuse is our natural instinct but it doesn't help us identify who does these things, how to treat or deal with them criminally, it just drives this further underground and into the darker recesses of the internet where it is flourishing extensively.