documentclass{article}
usepackage{everypage}
usepackage{ifthen}
usepackage{lipsum}
newififprintodd%<- false by default
letoldSectionsection
defhidesection{nullfontstepcounter{section}}
newcommandshowsection[2][]{normalfontoldSection[#1]{#2}}
renewcommandsection[2][]{%
  % Check if current section is odd numbered
  ifoddthesectionrelax%
      % Check if we should print it
      ifprintoddshowsection[#1]{#2}elsehidesectionfi
  else%
      % Current section is even. Check if we should print it
      ifprintoddhidesectionelseshowsection[#1]{#2}fi
  fi
 }
% Uncomment below to switch
% printoddtrue
begin{document}
    section{First}This is shown when printoddfalse is called.lipsum[1]
    section{second}This is shown when printoddtrue is calledlipsum[2]
end{document}