Dan Jones: Floyd Mayweather Jr vs Manny Pacquiao can't be another sporting 'what-if'

Sports fans love to play what-if. You know what I mean. What if?Barcelona (c2012) played Brazil (c1970)? What if? Ayrton Senna raced Sebastian Vettel? What if? Geoffrey Boycott faced Mitchell Johnson? What if? Bjorn Borg played Roger Federer? Etc. What-ifs are thought-experiments. They offer new ways of looking at familiar subjects. They?re also amusing parlour games, bantered between enthusiasts for fun. They aren?t limited to sport (what if Napoleon had fought Alexander the Great?) but sport?s…