Presuming God will not often forgive a repentant sinner, when that’s simply not the case in Christianity.
If you’re going to argue against Catholic doctrine, it’s important to do so in a way that does justice to that doctrine.
Jesus Christ died to atone for ALL sins so that ALL people might have the opportunity to go to chose the fulfillment of eternal beatitude in heaven (John 3:16-17; 1 Pet. 3:9).
In addition, sins that cry out to heaven for vengeance do not mean that one has who committed such sins cannot be forgiven.
The only unforgivable sin is final impenitence (CCC 1864). Further, mercy can sometimes be redemptively severe, as can analogously surgery or rehab after an injury. In other words, the purgative process–whether on earth or in heaven–is lovingly designed to purge unhealthy attachments that diminish a person and thus impede their true fulfillment in God (see CCC 1030-32; 1471-73). And so purgation can be redemptively painful. Thus, in a sense that the rock group Nazareth might not have considered, “Love hurts” sometimes.