As I understand it, when someone confesses a sin in the confessional even if they just have imperfect contrition, they are still forgiven.
Yes, that is part of the grace of the sacrament. Outside the sacrament, provided the desire to confess is present, perfect contrition avails the forgiveness of sin. Of course, it must be interior, universal, supreme and supernatural as the
Baltimore Catechism linked here lays out.
So does that mean any sin is forgiven in the confessional?
Definitely, for the blood of Christ cannot be overcome by human sin, nor does God will the death of the sinner, but that He be converted and live. To understand this you need to make the distinction between the guilt of sin and debt of punishment.
Guilt merits eternal punishment and as such is removed wholly or not at all. There is no stage in between. This is also the reason why if a person deliberately witholds but one mortal sin in the sacrament of reconciliation, he is not forgiven at all, does not enter a state of grace, but remains in the state of death, and moreover, commits sacrilege. For either all sins must be forgiven or none of them are.
But as regards the debt of temporal punishment, this may be undergone either in this life through civil law or in purgatory where it will be several times worse, although the holy souls there are still in the love of God, their purification, according to the Saints is more severe than punishment or imprisonment here.
Now, even after the guilt of sin has been forgiven, for the satisfaction of divine justice, penance is prescribed in the confessional.
What about some of these ɧoɱosɛҳųαƖ novus ordo priests who raped literally hundreds of boys, are they forgiven if they just went to confession?
Yes, they are, the eternal punishment is loosened, the temporal punishment remains in proportion to the sincerity of his contrition and the penance he performs, and if he passes this life without making sufficient satisfaction, again, that is why there is a purgatory.
That just doesn't seem right to me.
For my thoughts are not your thoughts: nor your ways my ways, saith the Lord. Does the priest have an obligation to find out who he is and warn his parish for the public safety issue?
if I refused to give absolution for certain sins that I felt were not up for me to give absolution to
Never. The seal of the confessional is of divine law and he who violates it excommunicates himself from the bosom of the Church. The sins of the penitent are strictly speaking for the Lord's ears alone, He it is who acts through His priest in forgiving the sins. The priest cannot reveal it in any way to anyone.
He may, however, prescribe a duly appropriate penance, for the grave and serious sin it is, and moreover direct that the man show a firm purpose of both restitution for his past wrongs and complete amendment in the future by impressing upon him the seriousness of what he has done.