"Is a professed religious faith necessary for one to live an ethical life? "
No, but.
People may live "ethical" lives based on their natural disposition and/or upbringing in a culture influenced by ethical norms. But never embrace, profess, acknowledge or even consider the real religious (or philosophical) ROOTS of those norms they live out.
Like a person who wheres clothes like everyone else but never questions WHY we do it the way we do.
"The corollary is does adhering to a religion ensure an ethical approach?"
No, "ensure"? No, never has.
Make it more likely? Yes, in the right circumstances.
Adhering to a good religion lays a foundation for WHAT IS ethical that's clear (for the most part). It does not leave most ethical questions open for debate. But whether or not a person, the bulk of a religious group or a culture LIVE those values out is another story. It's more likely If the ethical standards are PROMOTED and lived out by example by the leadership, in the religious group, the fathers, and broader culture. today the media culture. And sincerely passed down.
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Red points out "what do you mean "ethical".
At this point in time the clearer jeduo Christian definition is just the old MOLD that todays western current ideals are barely shape by. But it's still a real facsimile. As you mention not lying cheating stealing and killing are still adhered to and aspects of human equality and the santitiy of life . But all those are even questioned by some at this point even though most would claim they still agree with them.
My point in the atheism thread is that Atheist have nothing to go on but there OWN personal standards (mostly picked up in their culture) .
But finally the cultural ethical standards are BS ad hoc social structures for humans to get along with. Cannibal societies got along and had ethics. Societies with human sacrifice got along and had ethics. Those bad old missionaries taught them that eating people was bad and human sacrifice to false gods was bad. Against the rule of GOD. Ethics to an Objective standard.
Even the Irish were sacrificing children to false god's and drinking out of human skulls until St. Patrick and other CHANGED the ethics --the Faith-- of the culture. (mostly anyway).
In the 20th century the Atheist social darwinist taught that human kindness and not killing the weak was Anti the reality of our evolutionary mandate. That the strongest and fittest should survive. Lying, cheating stealing, killing were OK if the ultimate goal is the survival of the "highest" races.
Other Atheist ,who don't agree have no "ethical" base to refute them on. ethics for them are personal and made up by the societies. If the society decides it's wise and good to kill handicapped children then THAT is not just legal it's "ethical" since they can claim no outside objective standard.
Athist like richard Dawkins says he doesn't LIKE social Darwinism but he he has no good reason why it's "wrong". But he still says that our evolutionary natures compel us to survive above all and evolution's made us so only that animal urge will dominate our actions. Though he somehow HOPES we can RISE above it ..."somehow".
sorry its long
It is proper to take alarm at the first experiment on our liberties. The freeman of America did not wait till usurped power had strengthened itself by exercise, and entangled the question in precedents. James Madison
Live as free people, yet without employing your freedom as a pretext for wickedness; but live at all times as servants of God. 1 Peter 2:16