O am not trying to make you feel guilty. If you DO feel guilty then that is all on you. Only you can allow someone to do that to you.
I am just stating my opinion like you have stated yours. That being said, if you buy your supplies from a store that sells animals, you are supporting them. You are allowing them to continue to treat animals as merchandise.
Your thought process regarding your animals not getting the proper diet if you don't shop their doesn't hold water. You can get everything you need on line. Many feed stores will order it for you if you ask. So, in my honest opinion, I feel you are making excuses. I'm not trying to make you feel guilty, just stating MY opinion.
If you spend 25 cents at a store that sells animals, you are allowing them to continue and are putting a death sentence on animals in shelters. And that is NOT just my opinion. That is a FACT.