Although it should be, moral cowardice isn’t an impeachable offense. Roberts will just live with the shame.
Actually that's debatable. The US constitution has different qualifications for the terms of a SCOTUS judges than it does for other branches of government. The US Constitution says: The Judges, both of the supreme and inferior Courts, shall hold their Offices during good Behavior...
The Constitution does not define the term "good behavior." This means that moral cowardice, constitutional subversion, abuse of power, or any other crime can constitute bad behavior if it can be reasonably defined as bad behavior. Consequently, if a majority of the House votes to impeach and requisite votes in the senate feel that moral cowardice has constituted bad behavior, a judge can be removed from office. The founders did not intend judges to be impossible to remove from office, only difficult.
The Obamacare decision constitutes a serious abuse of power for which the majority needs to be taken to task. One of the major reason the court has become so lawless is because Congress has refused to use the threat of its impeachment power for so long.