[zo1]

"In a fair world we would allocate funds for medical research based on number of people suffering from illness and not their purchasing power -- but then the world isn't truly fair to everyone."

Agreed, it's really impossible and on the same shelf as "Perpetual Motion". But, to be fair, when most people these days talk of fairness or just, they mostly refer to their own personal notions of those terms and what physical outcome represents them best. The end result is that the terms are basically meaningless, as no one can reconcile their personal definitions with a global/universal definition (if one even exists).

"[..]And everyone including the government decides to fund research on disease B -- won't that be unfair and unjust ??" I'd say that sucks for the "large percentage" of people you speak for. But, then again, a discussion of this hypothetical scenario would devolve to a discussion of politics, because their government is supposed to represent majority interest. i.e. That's the actual problem.