Have you ever explained something with both logical and detailed precision only to come-up against a person who dismisses all the evidence you offer them by saying, “Its all a mystery.” Its dumbfounding how people may hide behind this word, abuse it, and wrongly apply it to matters that are already settled around reality and God! But this simply reveals the real temptation behind nominalism - it frees us from committing our mind and heart to a concrete reality: truth and goodness. If we can say, “I simply don’t know,” about things which we actually do, we chain ourselves down to the whims of passions or some rationalistic attempt to be consistent for no purpose at all. This is a type of darkness that sinners prefer to subsist in - a place where our actions may or may not be wrong. We lose touch with the very fact that we are relational beings, and identify as hedonists (who use the term love to objectively denote this) or we become rationalistic computers. In both of these cases, we forget that we are built to know and love.
We cannot acknowledge what we do not have knowledge of; nor can we love what we do not know. When it comes to loving others, and God, if we are spiritually being nominalists, we are always loving something superficial - and never the actual person. The reason for this is due to the fact that we cannot love what we do not know - love always precedes from knowledge, otherwise we might ask why and what it is we are loving?
Nominalism and/or Hume’s doubt is the "well-duh" view for a lot of post-modern philosophers. In a sense, it is considered to be a great advancement in philosophy, and with its many cheerleaders, its acceptance is more of a social paradigm than a critical one. That is to say, a beginning assumption for a lot of philosophers is the belief that the essence or nature of things simply cannot be known if it exists at all.
Putting this next to St. Thomas Aquinas’ anthropology which states that man wants to know and be known, we find ourselves in a somewhat problematic place. His point is that the "intellectual appetite" can only be satiated by goodness/truth. But if the nominalist is correct, and we can only know around things, but cannot really know about them in themselves, then the appetite we have will never be satiated and man's existence is hungering for something that either cannot be known or doesn't actually exist.
We cannot know the essence of one's lover (spouse), we cannot know the essence of a friend, we cannot know things of less value, and we ultimately cannot ever know the substance of God.
If this mindset is engrained within people, contemplation dies, and nominal faith, nominal relationships, and nominal commitments arise. Furthermore, a type of doubt will be cast over man's own experience of reality that is rather unhealthy, unreasoned, and ultimately disconnecting us from that spiritual dimension that unites the human race.
We must return, as Catholics back to the non-nominal, concrete, specific assertions of our faith. And we begin by asserting a God who is not merely a mystery, but one that is also revealing Himself to us. He is Father, Son and Holy Spirit - and these things we can state as concrete, revelatory facts about God's own inner-life. We likewise must speak of the nature of man and woman in His likeness, which can be known in itself, through sense, experience, and simple reasoning.
If man has a nominal understanding of God, he has a nominal understanding of himself. And if man does not know who he is, he cannot know others who are like him. And if man can finally know neither himself nor others, he cannot love either. We cannot know what we do not know. We can only end up loving what is about a person, but not the person in themselves.
How does this manifest today? I believe it can be found in the hypothetical culture - where we perpetually maintain a hypothetical approach to reality, to relationships, and to our understanding of reality. We, unlike the Blessed Mother, do not treasure the facts of Christ’s life in our hearts. We end up with a dulled appetite for truth and goodness, even within persons, Divine or human. Might I suggest, that the word “if” becomes a source of great distress in the spiritual life. It is the first word spoken by the Devil to Christ in the desert, and likewise it is often his first word to the Church. If you are loved by God! If you are a beloved son or daughter! If God is real! If the Eucharist is real! If… Any faithful Catholic will obliterate this word if at its onset, not as an avoidance of critical thinking and investigate, but as operating within the sufficient knowledge and revelation that God has already poured out upon His Church. Look to the Crucified Lord and see how there is no if in what He did. Look to the witness of the Apostles and see that there was no if in their belief in the Resurrection! Look to the beauty of His created universe, and its natural law and see no ifs around its laws! It may be tempting to hold onto these ifs to supposedly free us to operate in reality as we’d prefer it to be. But in reality it simply disconnects us from who we are, and engaging us our imagination in a room of darkness of mind.
I like your discussion of the “if ” - hypothetical culture.