It's not just about "grass fed vs. corn fed." It's much more complex.
When huge amounts of cattle are kept in huge feed lots huge problems exist. These feed lots are barren mud or dust filled enclosures with little room for the cattle to move around. The one's I've seen in OK, TX, MO contain hundreds, maybe thousands of cattle. If you packed them all in at one end, they would still fill up a third or so of the space. The biggest problem this presents is disease. To combat that, they barrage these cows with antibiotics. Do you want large doses of antibiotics in your meat?
These cattle producers work on slim margins. They use every trick in the book to produce big fat ladened cattle. That includes the use of growth enhancing drugs including hormones. Do you want growth hormones in your meat?
The corn that these cattle are fed is another story. Corn producers basically run corn factories. You can buy 50# of corn at the feed store for $6-7. The feed lots pay a lot less. Do you know how much it would cost to produce 50# of dried corn in your backyard? Imagine the regiment of fertilization, weed control, pesticides, fungicides,etc. these corn factories employ. Do you want this chemical cocktail finding it's way into your meat via the food the cattle are fed?
Managed pasture fed beef has none of the nasty stuff that goes into your supermarket beef, including the after processing additives that some use to increase shelf life.
Managed pasture beef is pure unaltered meat.
It's not as fat and marbled as feed lot beef. It also doesn't have the corn fed taste that Americans are used to and consider a positive thing.
It just tastes better and is sooooo much better for you.
There is lots of info on the internet. Do a search if you're interested.
Oh, and those "happy cows" from California. BS. Most dairy operations in the central valley of CA are feed lot operations where conditions exactly as described above exist.