The purpose of the sacraments is to strengthen our assurance of salvation, not decrease it.
Suppose there were no “visible channels” to convey an inward grace. We just lived as Christians the best we know how. Would we know if we were being “good enough” or if our faith was truly authentic? Some people - spiritually “high” people - might feel subjectively convinced they were in God’s grace, but feelings betray us all the time. You don’t have to be a Christian to know that. You just need to be a human being.
So rather than having scrupulosity, or presumption, the Lord has given us tangible ways of receiving grace. He also makes the sacraments social. Meaning: it’s not “Jesus and me”. The work of sanctifying the world is a mutual effort of the entire family of God. Even in Reconciliation, the most private of the sacraments, there is still always three people present: the penitent, the priest, and Christ.