1/3-2/3 (depending on the study and wording) don't believe that Jesus is truly present in the Eucharist. This is much more concerning to me.
That is part of the problem, yes.
IMHO, the position you state is legalism. What you seem to be implying is that if folks cannot pass a catechism test on the Mass-as-sacrifice, they are doomed.
The implication "if folks cannot pass a catechism test on the Mass-as-sacrifice, they are doomed" was not present in my post, and even if it was, that is not legalism; that would be Gnosticism. Legalism is a mindset where the person does one thing and is automatically reciprocated reagarless of any further actions or intentions; that was the mindset that people were adopting toward "x days indulgence" for saying certain prayers, and so the Church stopped publishing those indulgences.
What I did say was that a lack of understanding of the Mass-as-Sacrifice leads to Catholics not knowing why the Church commands the individual Catholic to go to Mass on Sundays and Holy Days; your conditional-statement should be revised, then, to "if folks cannot pass a catechism test on the Mass-as-Sacrifice, they will not understand the reason that the Church commands Catholics to go to Mass on Sundays." That is a much different implication.
The Mercy of Jesus is not based on our passing a catechism test. It is not measured by the number, severity, and timing of our sins (worse close to death). The Mercy of God is based on His sovereignty. We have been promised that if we cooperate with the gift of faith, we can then hope for eternal life with Him. So, Jesus will look into our hearts.
What you've written here is not wrong, but you are missing quite a bit, and, quarkily enough, are falling close to legalism yourself. It's always interested me that most people, while decrying legalism, then go on to describe the method of salvation as essential legal and dualistic. I'll explain why my position doesn't fit the label of legalism, and then say what I mean by dualism.
On legalism: A sin is a violation of a Law, of course, but since God is primarily Father, Son, and Holy Spirit (rather than Judge, Jury, and Executioner), the primary context of sin is relational. By sinning, I am rejecting the Fatherhood of God prior to rejecting His Sovereignty. That is why the prayer where we say "Forgive us our trespasses as we forgive those who trespass against us" is addressed to Our Father, rather than Our Master, or Oh Divine Judge. The act of forgiveness is profoundly relational - but then, so is the act of holding a grudge. By discordant relationships, the Christian who holds a grudge against another also throws out of harmony his own relationship to God - which is in far greater need of forgiveness from God, then his neighbor is from himself (charmingly depicted in Jesus' Parable of the Unforgiving Servant, Mt. 18:21-35). Because of this, then, when you say "cooperate with the gift of faith," I fully agree; and sinning is not cooperating with the gift of faith. Cooperation with the gift of faith is something relational and affected by the individual's actions, and so we cannot separate what Jesus finds when he looks "into our hearts" from our daily actions, which yes, does include "the number, severity, and timing of our sins." To separate the daily action of human life from the state of the heart is to espouse a legalism where the salvation of God is a matter of legally glossing over sins - as if the sins were merely a legal - and not a relational - matter. With that in mind, consider the legal obligation of Sunday Mass through a relational lens: by participating in the Sacrifice of the Mass, the Christian is brought into the most profound relationship to the Divine that he or she could be. It is the duty of the Christian to rise with Christ, and this is effected most completely in participating in the Mass; on the other hand, to choose to do something else when the person is otherwise able is to turn away from that relationship.
On dualism: A temptation in modern spirituality is to over-subjectivize spirituality. Separating daily action from the state of the heart is to make two separate realms: the realm of the spirit, which is seen primarily as an interior "me and Jesus" thing, and the realm of the flesh, which is seen as, at best, only a shadow of something More Real. Consequently, most people excuse themselves from certain obligations (including alms-giving, going to Mass, and not gossiping) by saying "oh, God knows my heart," or "He understands." On the contrary, the Thomist philosopher Jacques Maritain says that the Christian is called to something he coined as "Active contemplation;" it means that the actions of the Christian in daily life stem from the Christian's prayer and relationship with God; and if there is no "contemplation" then there is of course no "active contemplation." To choose to go to Mass is an aspect of the "contemplation" side of the term, and its effects are metaphysically inscribed in the soul.
Unfortunately, a large part of the "accept Jesus as your personal Lord and Savior, and then yer' all set!" theology has penetrated the Catholic mainstream. That notion is the most legalistic of them all, because it envisions a system where, no matter what I do in my daily life, my relationship with God is static and unaffected. The Catholic theology, on the other hand, claims that my actions
do in fact dynamically affect my relationship with God - for better or for worse. A priest once told me "All human life is an initiation into the eternal," and I completely agree. Its an initiation into the life of God, and that initiation is never static.
And just BTW, the understanding of Mass-as Sacrifice is not the only view of Scripture. The Orthodox reject this as a late Western addition to dogma.
Remember the last time we were talking about a difference in theology between the Orthodox and the Catholics? The same thing then applies now: the Catholic theology lays the reason for why Catholics are required to go to Mass on Sunday. I do not know the Orthodox theology, but this is the way it developed in the West. Consequently, it does not matter in this particular case what the Orthodox theology is - the Orthodox theology is sufficient for the Orthodox, not for Catholics.
