The Mike the Chicken thing just sounds sick and inhumane. If you are going to kill a creature, then just do so. What some idiots will do!
As for the 3-legger, I wonder if there is some way to have the extra removed if it is getting along alright otherwise.
To McMurrays defense, depending on where it is located, they may have missed it if it was in a straight run bin. That being said, I am still surprised they wouldn't have seen that. Where is the QA? Then again, they are zipping 80,000 chicks through that place every week, so I am actually surprised there are more incidents. I don't think that any hatchery is perfect, I see bad comments on every one. I had great luck with MM last year and have an order coming next week. I have ordered from Sand Hill Preservation and so far, they aren't getting high marks from me.
To the OP, as long as your chick is healthy otherwise, just keep it going. If it is a Cornish cross or something of that nature, it is destined for the dinner table anyway.
I hate to sound cold, folks, but not everyone has an emotional attachment to every critter they have on their farms or in their backyard. It is all part of the great circle of life.