Congress bans the CDC from doing study on gun violence

[Angrboda]

Linking serial shooters to mental illness is pointing the arrow of inference the wrong way. Perhaps there is something wrong with serial shooters, but you're identifying them from the act of serial shooting, not from their being mentally ill. From the fact that one is a serial killer, one may infer that something is wrong with serial killers. You can't infer the other way around that if someone is mentally ill that they are more likely to become serial killers. That's not a valid inference.
serial killer ------> mentally ill
mentally ill --//--> serial killer
All you're doing by increasing treatment for mental illness is helping people get well, not preventing spree shootings like in Oregon.