In Denmark they banned sub therapeutic use of antibiotics in an effort to stop resistance in humans, but it has basically failed after an entire decades worth of data was analyzed. And since some of the antibiotics that were showing levels of resistance weren't even being used in the livestock industry it stands to reason there are other factors, one of the being hospitals.
Banning antibiotic use can also end up being more expensive for the producer and less productive which will raise food prices way up. In addition, since the sub therapeutic antibiotics were banned, it was sometimes necessary for veterinarians to prescribe even more therapeutic drugs, leading to a higher level of antibiotics being used than if they were allowed in moderation to begin with.
Sure, a ruminant has a digestive system that evolved to eat mostly high fiber content, but today their diets are closely monitored at feedlots. Feeding too much grain CAN cause acidosis which would cut into their profit if they had to treat all the cattle people think are being pumped full of too much grain. And I hate to break it to you but even organic food can be a GMO.
I agree that feeding large amounts of livestock in smaller areas is not IDEAL but it is necessary in order to continue being able to feed our growing population. Grass fed beef, while it has slightly higher levels of Omega 3's, is not really that much more nutritious for you and it is actually less environmentally friendly than corn fed beef due to the amount of land needed, taking longer to grow, methane emmisions, etc. If you would like to read about that more look up work by Judith Capper.
Most of the "healthy" "organic" "natural" stuff is marketing nowadays. Slap a label on it and people will buy it thinking they are eating healthier or being environmentally friendly when that isn't the case at all.