The problem with this reasoning is that when a person sins, his/her conscience becomes defiled. It's GOD's way of letting us know we've done something unrighteous. We can't just ignore a defiled conscience or it will become seared. Acknowledging the truth allows forgiveness to cleanse a defiled conscience.
I've heard one person say that for a Christian to sin is like a fish out of water. It doesn't belong. We may sin (as John said "If anyone sins...") but we, as believers, walk in righteousness. If/when we sin it does weigh on our conscience, and what usually lifts this weight is making amends (as some have brought up).
Some people feel that they must seek forgiveness for sin, after committing it, where as others believe they are forgiven, express apologies, and move on. It is through this expression that often our own guilt is lifted, especially is the case when we believe ourselves to be in some way condemned by God (eternally, or even relational). So they repent, confess their sin, and because they believe God has
now forgiven them, all is well. The negative emotions are lifted.
What is the difference between the person who believes God has forgiven them already, and the one that seeks forgiveness? Peace! As for the defiled conscience, would you not say that such feelings are far more extreme for the one that believes a penalty is to be incurred? They are in fear, and their conscience weighs heavy as a result of such belief, as opposed to just their conscience bearing witness against them (as they know better). There is a difference between a healthy/pure conscience and one that is oppressive as a result of false doctrine.
Either way, and again, many of us here have already stated that they confess their sins (not for forgiveness) and so even under your premise, of not acknowledging the sin would lead to a seared conscience, people do acknowledge their sin. The only difference is that they aren't seeking forgiveness from God but transparency unto victory. They do not hide their sin, a silly endeavor.
Therefore your conclusion as to what my reasoning would lead to is incorrect. God's grace (and forgiveness) won't lead someone to a seared conscience. In fact, under such reasoning it would lead to a healthier conscience (not being oppressive due to condemnation, eternally or on a relational level). God's forgiveness, already being given, doesn't desensitize us to our wrongs. We still acknowledge them.