I think one could potentially drive oneself to distraction analyzing such detail of every action (or inaction) that one takes. I think its good to consider such questions, but do not agonize over it. Ultimately it's up to you to decide what actions and inactions are best to take (or not). You have to consider the overall picture of providing for yourself and your family, as well.
But then, I'm not a vegetarian, and don't really understand the difference between killing an animal for self-nourishment, and digging up a potatoe (which kills the plant, doesn't it?) and eating it. The cycle of life is meant to provide for us all, and we for it. It's when waste and greed come into the picture that something is 'wrong', in my view of things. (And fastfood is both.. this would be more my concern.. the litter and poor nutritional value of the food!).
Anyways, that's my 2 cents of thought on the matter, for whatever it may be worth to you