I do not want to kill a cow personally, but I am aware meat I eat comes from cows. I would be against law that would make cow killing illegal. Not wanting to do something personally and accepting it happens for food is not cognitive dissonance. In general, I am ok with killing animals for food. If you killed a cow just for fun or sport, you are an asshole and I am against it. I feel no cognitive dissonance here.
Likewise, I am pro cleaning shit out of places. I prefer when someone else does it.
If you want to understand my point about dissonance, you might substitute "dog" for "cow".
Or you could look at why you wouldn't kill a cow. For me, I would feel pretty awful about it. I think, for example, about the time I had to take a dog in to be put down. It was necessary, and there was no other choice. But it was fucking awful to take that dog in and have it killed. Cows are lovely animals in person, and I would feel like I was betraying one to kill it.
So for me there would be a lot of cognitive dissonance generated by killing a cow to get food when I have plenty of less murdery ways to get food. I avoid a lot of that dissonance by outsourcing the job, but some of it's still there.
Likewise, I am pro cleaning shit out of places. I prefer when someone else does it.