Speaking of having only one doctor... thats another reason he shouldn't have "killed" the Equinox EMH, just disabled him and reinstated his ethical sub routines.
Where's the hue and cry over him killing his "brother",
a "being" that was mentally savaged by his crew (as much as "our EMH was savaged by Ransom) that Janeway has to deal with over Tuvix?
I would imagine that there was only one EMH because you hope to never have to use even the one. He was designed to be used in an emergency only and for a short time. Even still his program was very large and it might be that having two of them would take up too much space