Well, you wouldn't eat "only" horse meat for one, venison has no marbling either and considered very healthy.
HORSES ARE NOT BOTTOM FEEDERS.
Goats eat anything, we eat goats. Catfish, carp, pigs, hell even cockroaches are regarded as food depending on latitude/longitude.
Your fear of eating something not widely used as meat in our country is while understandable based on irrational and illogical thought, unfounded.
There's far too much hunger in the world for me to toss out 1000 lbs of edible and healthy food. Even if it was full of mediccnes, it's better than starving. You should give it a shot and see how quickly you'd plow through a horse burger...