Cure cancer or cure depression? Depression leads to cancer, and cancer kills. Also don't forget that SCP 999 can also pacify serial killers so murder rates would go down. Also since SCP 999 is a slime with more personality than you it can divide down into 2, 4, 8, 16 and so on. Depression leads to a total of 850,000 deaths every year and murder leads to a total of 400,000 deaths every year. Adding those numbers up leads to 1,250,000 deaths from the two every year combined, while cancer only kills 600,000 people a year. Turns out the only stupid one is you.