I'm surprised that the rate of non-completion was in the order of 20% in the Blind Print Exchange. I've been in two rounds of Group Print Exchange and received all those expected (despite most of them having to come from overseas) and the Postcard Exchanges also seemed well covered - although I can't say I actually counted them.
20% is unacceptable and those responsible need to find a very good excuse for their inaction. No doubt some do indeed have one. Quite possibly, some do not even realise they are on the list and thought their prints were received months ago. PMs and emails go astray; people change their email addresses and forget to notify everyone involved; people may not wish to tell of private tragedy or life event, etc, etc, etc... The human capacity for misunderstanding and lost communication is practically endless. Calling people names is not a recipe for resolution of an issue: it simply hardens attitudes and will frighten those with a valid reason in to silence for fear of public hostility.
So, my view would be to stop calling people names, ban offenders (I'd say at the 1st offence rather than the 2nd) until the outstanding commitment has been honoured or otherwise dealt with to the contentment of all involved. If people do not meet their commitments, I have no interest in knowing their names; a deeply unpleasant concept akin to public flogging and humiliation that belongs in a different age.