The issue is generally that grass-finishing is slower, so cows (may) end up producing more methane overall.
However, grass-fed is definitely better from an animal welfare perspective.
Some of your other claims seem difficult to support; for example, I'm not sure it's well-understood what is driving obesity, and so claiming that it's corn seems like a bit of a stretch. Similarly, corn does actually have nutritional value, which is why people have grown it for a very long time, even before subsidies.
> The more time grazing livestock are housed, the smaller the proportion of their excreta deposited on grazed pastures will be, and hence the smaller the emissions from those pastures.
[0]: https://www.eea.europa.eu/ds_resolveuid/8e90ca718fd34d5786c1...
High Fructose Corn Syrup, no ?
It would be an interesting thought experiment about what would happen to obesity levels if prices were taxed to the point where the price difference would be eliminated.
This seems obviously false.
Regardless, according to google, you can still eat field corn if you want to and it still has nutritional value.
> The word "corn" outside the US, Canada, Australia, and New Zealand refers to any cereal crop, its meaning understood to vary geographically to refer to the local staple. In the United States, Canada, Australia, and New Zealand, corn primarily means maize; this usage started as a shortening of "Indian corn".
I (from the US) learned about this when a botanist pointed out that the movie "Fellowship of the Rings" incorrectly depicted maize for what Tolkein described as 'corn' in the Shire. http://tolkiengateway.net/wiki/Corn
The most destructive thing, farming wise, we do... is the corn industry. Ruining soil faster than any other crop? Corn. Using so much water in the midwest that it makes California's water shortage look competent? Corn. Polluting the waterways with commercial fertilizers, resulting in, but not limited to, the dead zone of the Gulf of Mexico? Corn.
Does corn have any nutritional value to humans or our livestock? Nope! Does it produce anything valuable for industrial purposes? Nope! Would it continue to exist without the trillions in subsidies we've paid over the past decade? Nope! Is it one of the primary drivers behind the obesity crisis? Yup!
Can't print that headline though, rich people get angry when the truth collides with their Scrooge McDuck-esque money vaults. So, "feeding them seaweed" as a "think positive" headline workaround continues to get the word out, albeit in a strange way.