Hello.
I also keep rats as pets, and mice as food (and pets). Most of the mice have names, and I pet them on cleaning day. I do not have a problem seeing Smokey or Panda being eaten when I know they had as nice a life I could provide, and a quick death. I use the CO2 method. You have to decide what you are comfortable with. No one can tell you how to feel about it. Be kind to them and you will feel better about helping along the food chain.
Feeding (what and how much) a monitor is just one of the decisons you will have to make, along with housing, handling, and pairing. There is no perfect established way to keep them, and everyone argues their points.
That said, rodents may not be a natural diet, but it is a proven to be good one.
Wild ones have thrived eating human garbage, and captive ones have survived eating wieners (hey, human garbage!) How healthy do you want your lizard to be?
Iguanas are very nice, too. They eat vegetation.
D.