#1- There is no guarantee that I would be getting my own animal back. Even at our local slaughterhorse in Hilo, you're not allowed to watch the process. You have to drop the animal off then return a couple days later to pick up the wrapped meat. I've talked with a few neighbors who swore that they didn't get their own meat back. There's no way to prove that, but it's what they believe. Since the slaughterhouse sells meat to stores and restaurants, and processing is done behind closed doors, and there is no third part inspection or supervision, the benefit and opportunity to the slaughterhouse of switching carcasses surely exists.
#2- Animals go through mental and emotional stress when transported if they have not been conditioned to it. I've seen them "dance" in trailers, repeatedly crash into the trailer sides attempting to escape, repeatedly vocalize, get "stress diarrhea", hyperventilate. Why put them through that if there is no need?
#3- Since I would never sell my livestock via an auction or to a slaughterhouse and thus into the commercial meat flow, I won't even go there. That's a situation I can never approve of, though I have been forced to condone all my life via eating commercial meat and eggs. In the 80's and 90's the commercial situation was atrocious. Thankfully Temple Grandin has precipitated dramatic changes and improvements since then. Hubby chooses the bury his head in sand when I comes to this issue. We can't even discuss it.
#4- With properly done home slaughter, the animal undergoes little or no stress or pain.
#5- As was pointed out to me by a neighbor, once you're set up for it, home slaughter and butchering is a heck of a lot cheaper.
The down sides are:
...often people cannot deal with the emotional aspects.
...you need to learn from someone else how to do it.
...you cannot legally sell, trade, or in some locales even give away or share the meat, depending upon the species. But to tell you the truth, most people I know that home slaughter & butcher ignore that regulation.
...with larger animals, you need to have a big enough freezer for storage
...for beef, you need to arrange to have the meat hung for aging since most people don't own their own walk in refrigerator.
I live in a area where home slaughter & butchering is common enough. I'm sure there have been many a tourist freaked out when they pass by one of these events. But locals here generally accept the idea.