Simple... they have no idea that their actions are stupid. They have a perception that their behaviour is completely normal because that's how they've been behaving for all their life.
I've never tried them but I know a little about the subject. SSRI's stop the Seratonin reuptake transporters. It causes less seratonin to be reabsorbed so there is more present in your brain. I've never tried them but I know that you need more than just the pills to make any significant difference and they take weeks to effect your mood.