IMO it isn't right to keep an animal suffering that has no chance of recovery. I don't have a problem with putting them down. If they are still useful to man afterwards I don't have a problem with selling them for meat either though. It would seem a waste not to. What does concern me is what you have posted about the way they are treated during the process. I had not heard of this before. The only slaughter I have ever been around was a pig and some chickens and it was instant and they didn't suffer. My husband was very emphatic about this. He stessed to my sons to do it right or not at all. I would like to know more about these conditions if you have links though because in the short period of time I have been around horses I notice they do communicate and feed off each others fear :'(
I have ~seen~ links before that went to sites that showed what happens in sales and in the transport of the horses to slaughter. I have been to sales where these horses take the first step, and I have been to a 'ranch' where they go in between. (the guy also sold riding horses he could salvage from the sale).
I don't want to look now for proofs to show you because I try to protect myself from that. In truth, my ability to prevent any of it is limited, and I would rather not see it than have the sights haunt me. I know that is wimpy, but it is how I stay happy in a crappy world.
But the process is long, from sale to slaughter, and the distance to travel is sometimes long. With the acknowledgement that the horses are sometimes there because of the injury, know that they endured that injury for the many days and miles that it took to get them to the end.
There is another set of horses that end up in slaughter, and those are the premarin foals. I know only a little about the process of Premarin, a hormone replacement drug for women... but it stands for Pregnant Mare Urine. Mares are bred and kept in stalled conditions where urine can be collected and turned into this drug. Their foals are a side-effect not unlike the calves that are born at dairies... They just simply overflood the market where few want to take a foal that is newborn and must be nursed and raised by hand. The easy answer for Premarin is that there are synthetics already available that will be far easier and economical to make in the lab than it is to keep and feed a barn full of pregnant mares. That one will, I think, solve itself.