A concentrated corn ration can cause acidosis in cattle; that's why even for a steer, corn will make up less than 10% of the diet over its lifetime.
A feedlot steer fed a conventional feedlot diet will receive up to 85% corn over a 140 day feeding period. Assuming 20 lbs dry matter intake, that will be @ 17 lbs of corn daily. Yes, acidosis can (and does) often occur as calves are transitioned to higher NEg diets. The reason that occurs is because the ruminal population is not adequately ready for the large infusion of starch.
I said the comment was “stupid” because it was suggested that “cows” are poisoned with corn which is utter BS. If a person wishes to eat grass fed beef, more power to them. Just recognize that the flavor will be different and the product will be more costly.