By engaging with their arguments, seeing what they're based on, whether they really are what one ought to do, etc.
So, what do you do if you start from the same premises but then diverge? Is there an "objective" way to figure out who is right in absence of some mathematical theory of morality?
As per a recent comment this thread is meant to voice contrarian opinions, that is anything this community tends not to agree with. Thus I ask you to post your contrarian views and upvote anything you do not agree with based on personal beliefs. Spam and trolling still needs to be downvoted.