Right against self incrimination is more or less literally a right not to be tortured. Like it slightly disincentizes the pigs not to hurt you until you confess if there's a legal norm that you're not expected to confess.

Straight up, no bull; in my "why i come in to my power" confessions will not be admittable as evidence without corroborating physical evidence of some kind. You can use a confession to support other, existing evidence, but a confession alone ain't worth shit.