Did you skip the part about greater hope for salvation for ignorant Catholics who just follow orders than those who actually understand the faith and remain in it?
With all due respect, I think that the author was referring to individuals who are aware of the differences between Catholics and Protestants and still insist upon being Catholic contrary to their conscience. (I am not saying here that someone would NECESSARILY have a conscientious objection, but merely that it is what the author seems to believe)
As a Catholic you most certainly believe this about Protestants. The Catechism of the Catholic Church allows for "Invincible Ignorance":
1793 If - on the contrary - the ignorance is invincible, or the moral subject is not responsible for his erroneous judgment, the evil committed by the person cannot be imputed to him. It remains no less an evil, a privation, a disorder. One must therefore work to correct the errors of moral conscience.
This reflects what the author was saying in regards to faithful Catholics who do not question their beliefs. It's the same statement but flipped as it is coming from a Protestant applying it to Catholics instead of the other way around.
The Catechism also states:
1790 A human being must always obey the certain judgment of his conscience. If he were deliberately to act against it, he would condemn himself. Yet it can happen that moral conscience remains in ignorance and makes erroneous judgments about acts to be performed or already committed.
1791 This ignorance can often be imputed to personal responsibility. This is the case when a man "takes little trouble to find out what is true and good, or when conscience is by degrees almost blinded through the habit of committing sin." In such cases, the person is culpable for the evil he commits.
1792 Ignorance of Christ and his Gospel, bad example given by others, enslavement to one's passions, assertion of a mistaken notion of autonomy of conscience, rejection of the Church's authority and her teaching, lack of conversion and of charity: these can be at the source of errors of judgment in moral conduct.
It stands to reason that, from a Catholic point of view, a Protestant who has taken the time to examine what the Catholic Church teaches, understands the reasons it teaches such, and refuses to be a part of her is culpable of mortal sin and places his or her salvation at risk. That education has dispelled all appeals for claims for ignorance. This is exactly what the author was stating, albeit from a Protestant point of view.
Respectfully, it does little good to be indignant about a Protestant teaching the same thing regarding Catholics that the Catholic Church teaches regarding Protestants. The author left the door open for individual Catholics to be saved in exactly the same manner that the Catholic Church leaves it open for Protestants to be saved. It's the same reasoning albeit applied from a different point of view.