The medicine in chick starter is for coccidia, a protozoan parasite which causes severe diarrhea and death in chicks. Coccidia (sometimes abbreviated cocci and should not be confused with "cocci" as in "gram positive cocci" like Staphylococcus (bacteria) or "cocci" as in coccidiodiomycosis otherwise known as valley fever, which is caused by a fungus.) If coccidia is not a problem in your area, you do not need to medicate. I have never medicated chicks and never had a problem with it. It seems to be more of a problem in wetter climates. Not to say it can't occur in Arizona, just not as much a problem.
The other thing to consider as you raise your birds is your own philosophy on organic versus non-organic. The Purina feeds are not organic. That means the ingredients are GMO, genetically modified to resist Roundup. 90% of the corn, soy, canola, and cotton grown in this country are GMO and they spray the heck out of the crops with Roundup. So that chemical is in the feed. If you look on the ingredient list on the bag, I bet the top two ingredients are soy and corn. If you feel like a lot of us on this thread, who only feed organic, that the GMO, chemically-laden, feed is bad for us, then you do not want to feed this to your birds. As it will end up in your food supply eventually when you eat their eggs and if you eat their meat. The bag has to say "certified organic" on it, or it is not organic. None of the medicated feeds are organic