Yes, the Gospel is Good News; the best news in the world. But it is only good news to those who understand the bad news first, that they stand guilty before a holy God. Without that, the cross makes little sense.
As for Revelation 21:8, I don’t think it is limited to ‘those outside’ only. The verse is a warning to all who would shrink back in fear and reject Christ. That’s why Hebrews 10:38–39 also says, ‘If anyone draws back, My soul has no pleasure in him. But we are not of those who draw back to perdition, but of those who believe to the saving of the soul.’
Mark 4 shows that God, in His sovereignty, sometimes conceals truth, but He also commands us to proclaim it openly. Jesus told us in Matthew 10:27, ‘What I tell you in the dark, speak in the light; what you hear whispered, proclaim on the housetops.’
So, while the Gospel is Good News, it is a call to repentance, and those who suppress the Spirit out of fear or love of sin are in real danger. That’s exactly why we can’t afford to stay silent.