Dark Matter: What is it and how can we tell?

Dark matter is only inferred, not seen. It's not seen directly because it isn't emitting any visible light. Visible light in the universe usually comes from the reactions such as fusion within stars. No radioactivity, no light.  In a universe made visible by the radioactive decay processes of its components, the lack of visibility of significant portions would suggest those are no longer radioactive. Uranium when it "dies" becomes lead. Lead is heavy, dark, and fairly common. Much like "dark matter". Are we trying to reinvent the wheel?