My argument against horse slaughter is both emotional and logical, at least to my sensibilities. I am against it because I think we make a higher contract with horses when we halter them, bridle them, and say "trust me, work with me, and I won't hurt you." I think it is fundamentally unfair to send them to slaughter because they have been broken in our service. It's as reprehensible to me as selling my dog for meat when he becomes sick. My animals will never have that fate.
I cannot disagree with your statements. However, I feel there is a serious trap door to the idea that a horse is a "companion", as many animal activists want to declare them. If they are only a "Companion", I am afraid that they will next lobby and prosecute all of us horse owners because we "ride" them, "Race them", "Jump them", etc, etc,etc,. Beware of what we wish for, as there is often a trap door in the structure.
There is also the issue of being able to donate an injured horse for zoo meat or to places like the large raptor/carnivore rescue place in Los Angeles which needs lots of fresh meat every day for their rescue-rehab efforts. You cannot just try and talk to a lion or an eagle and talk it into eating Cheerios......
Very true, which is why I don't determine what's right or wrong based on what the extremes might want to do... They are just as wrong as the other extreme. The right answer is not necessarily the polar opposite of one wrong answer, and we usually find it somwhere in the middle.