The difference between "snitches" and witnesses. Bottom line, snitches receive some compensation: a reduced sentence, cash, privileges in prison, etc.
No one is for witness intimidation by criminals. Some of us just also oppose witness intimidation by police. If a defendant pays a witness for alibi testimony, it's tampering. If the prosecution pays a witness to bust that alibi (even if the "payment" is a reduced sentence, though sometimes cash), that's considered good police work. How is that just?