It's easier to make/process, use and analyze nanoparticles of gold than anything else, so it's the best characterized material. It's easiest to process and analyze because it's heavy and inert. And then for medical uses it's key that gold tends to remain nontoxic in any particle size/shape unlike most other nontoxic metals. Silver is not as good about being totally nontoxic in any formulation like gold, though interestingly sizing of silver nanoparticles show deposition in different tissues based on size (so the nanoparticles could do the targeting by virtue of their size/shape).
There's definitely incredible potential with the ability to engineer natural killer cells, no doubt about it. But I see a simpler and sooner available solution to HIV and other viral disease with DRACOs (altho it maybe only treatable with these in an early stage or as a 'temporary universal vaccine'). DRACOs (Double-stranded RNA Activated Caspase Oligomerizers) are the class of combo ds-DNA detection protein and a programmed cell-death signal protein. The combination makes the cell's automatic suicide process extremely sensitive to viral presence (preventing the cell from hosting viral reproduction). Only invented last year, these are still awaiting human testing, but they do appear to be a miraculously perfect cure/temporary vaccine for apparently ALL viral disease. These are pretty much the most promising looking antiviral drugs ever. http://web.mit.edu/newsoffice/2011/antiviral-0810.html
I don't think anyone would argue that Stalin or Mao were sane. Like so many leaders, they were homicidal psychopaths. MAD seems to have worked even despite insane leaders.