I have eaten horse meat overseas (a long time ago) and found it perfectly acceptable. However, where horses are not specifically reared as meat there will be no record of medicines and other treatments used, so the withdrawal times will not be noted, or adhered to. As for sending maltreated, malnourished, neglected horses for meat, then the meat itself is likely to be of poor quality and the parasite burden could be high. Surely if those same animals were cattle, sheep or pigs they would be rejected for human consumption at the slaughterhouse?
If we are to eat horse meat then it should be from animals reared and slaughtered in our own country and with the same health and identification requirements as other meat intended for human consumption.
Even then, if those selling the products are unaware that there is horse in their products then they cannot claim traceability.
I can't help but feel that those of us who can rear our own meat and grow our own vegetables are in a happy place, but for most of the population that luxury is unavailable so they have no option but to trust the shops where they buy their food. The problem here is betrayal of that trust.