Are upstairs air returns necessary in an older home (1945) ?

by Stan H
(Napoleon, Ohio)

I am having a forced air furnace replaced and AC added. The contractor says that air returns are not necessary on the 2nd floor because its an older home with draft through the walls (not tight).

Other people say it is necessary to cool the upstairs and not overload the system. So, are upstairs air returns necessary in an older home (1945)?