Sources: http://www.scientificamerican.com/article/premature-deaths-m... http://www.who.int/features/factfiles/malaria/en/
Milder winters expand the range of disease-carrying insects, increase risks of wars or famine with less water, mass migrations leading to political instability, more extreme weather events like draughts and flooding leading to failed crops and other natural catastrophes...
Meanwhile much of the WHO estimate is for people dying due to heat exposure. Easy to quantify, important to know - but nowhere near the full picture.
Malaria is unlikely to get much WORSE than it is now. But if you think that global warming has a chance to cause catastrophic damage, two or three orders of magnitude more than malaria is causing today, then you should estimate the probability that you can impact global warming and do the EV calculation.
How can the very lack of evidence and data logically support a claim that any estimate is either too low or too high with any "certainty"?