Their error is in equating “not good” with “bad” – as in the general admission that fast food is not good for us, since it is calorie-rich and rather nutrient-poor food. Not the same as bad – actively harmful, in some ways toxic per se.
Here is a continuum with 8 distinctions: extremely good is better than very good, which is better than good, which is better than not good, which is better than not bad, which is better than bad. Beyond bad there is very bad and extremely bad.
One fast food meal per day is not good for us, since it makes it harder to reach nutrient sufficiency without caloric excess.
Two fast food meals per day are most likely not bad for us, if the other meal (with high nutrient/calorie) compensates for fast food nutrient deficiencies and caloric excesses.
Two fast food meals per day are most likely bad for us, if the third meal is a store-bought prepared meal.
Three fast food meals per day are either bad, very bad, or extremely bad for us, since the chances of being nutrient sufficient without gross caloric excess are slim to none.