Preaching to the choir means you are trying to make believers out of people who already believe, or convince people who are already convinced.

The safeguarding of Earth and other worlds from biological cross-contamination (i.e. billionaires with too much time on their hands).

Also known as “planetary protection.” Planetary protection / quarantine “reflects both the unknown nature of the space environment and the desire of the scientific community to preserve the pristine nature of celestial bodies until they can be studied in detail.”

There are two types of interplanetary contamination. Forward contamination is the transfer of viable organisms from Earth to another celestial body. Back contamination is the transfer of extraterrestrial organisms, if such exist, back to the Earth's biosphere.

Spending time trying to convince people who are already behind you.

Extolling/defaming a cause to people convinced of it's greatness/horridness. Etymology is obviously from christian church choirs.