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Is it possible to persuade a person into changing their ethical positions using logical reasoning only?
Let's say person A is an altruist and believes in "greatest good for greatest number of people", and person B is a misanthropist and doesn't care for other people. Is it possible for one of them to convince another, that their position is false, invalid, unsound, and should be changed? On what does this depend?
The answer to this question depends on your position on the is-ought problem. David Hume argued that philosophy cannot logically deduce "ought" statements (statements of ethics) from "is" statements (statements of fact). Some philosophers disagree (see, e.g., Murray Rothbard's The Ethics of Liberty).
If you and your friend agree that there is no gap between is and ought, you should (in theory) be able to resolve your differences using deductive logic alone. If you think there is a gap, you can still use reason and evidence to evaluate the veracity and merits of the competing theories - just not in a way that's 'logically airtight'.
Greatest good for all is utilitarianism, not altruism.
Some psychologists would say it depends on the script they wrote for themselves in childhood. Everything they do and the people they surround themselves with is a way of validating their image of their role.
If the person is less sure about his guiding principles, he's going to be more resistant to change. The more uncertain someone is, the more they will defend their position.
One technique you could try is hypnotizing them to a regressive state and re-parenting them with better strategies. Not sure we're supposed to know that if we don't have ph.D's in clinical psychology or something.
Books you might like:
Persuasive Technology BJ Frog
Games People Play
