[globjgtyf]

How could a member of SCOTUS be deemed "unethical"?

All of those who sit on the court take an oath to uphold the constitution, which includes this interesting clause:

... I will administer justice without respect to persons ...
Seems that the Citizens United ruling fits that to a T.

Besides, who are we to question such an honorable citizen, who gives up his / her life to so selflessly serve the country?

Only one member of SCOTUS has ever faced impeachment: Samuel Chase. In 1805 he was acquitted of all charges (which dealt with his actions as a judge prior to his term on SCOTUS) and her remained on the court until his death in 1811.

The Chase case established boundaries that remain to this day: "All impeachments of federal judges since Chase have been based on allegations of legal or ethical misconduct, not on judicial performance."