In UK atheists considred more moral than theists.

[Angrboda]

Not getting our morals from someone who claims to be a moral authority. But asking this about atheists is a category error, as they same question would be if asked of theists (you'll get different answers depending on what god they believe in). On this forum, most of the atheists are humanists, who use their brains to figure out what is most moral based on what has the best outcome for human thriving.

*emphasis mine*
Really?

on this forum:

Some atheists were defending a gay man buggering an under age boy.

Another atheist has stated there 5 people she'd like to kill if she knew she could get away with it.

Another atheist claimed if he lived back in the day, he'd happily participate in chattel slavery.

(I assume you disagree with the above?)

Clearly examples of why an individual's brain isn't capable of deciding what's moral.

So again, what is an atheists moral authority?

Theists will argue, in defense of changing mores with regard to, say, slavery, that there being a source of moral values doesn't necessarily imply that we will have an unfailing ability to determine what those values are. The former is a question of moral ontology rather than moral epistemology. That there are varying opinions about what is moral does not imply that there is no such thing as a moral truth. Both theists and atheists make this point, so your questions are unenlightening. Moreover, if morality is relative rather than objective, morals may change over time or among different contexts. That doesn't mean that there isn't a source of morality underlying their determinations. Perhaps what you mean to say is that atheist morals are arbitrary. That may be the case, but even if so, they are no less arbitrary than the morals of a theist whose God pulled his or her specific moral rules out of their ass.