A secular account that avoids both "because I said so" and "anything goes." You give up the rulebook in the sky and keep a real floor under right and wrong.
It is the standard challenge to a secular ethics, and it deserves a straight answer. The two usual replies both fail. One points to a moral law written into the universe, but no one has ever been able to exhibit it, and every version has needed quiet revision as societies changed. The other says morality is just what a culture endorses, which collapses into relativism the moment the culture shifts.
Call a rock bad and you have to ask who it harms. Watch a person suffer and there is nothing to add. For a being that can feel, things going badly is part of the experience, not a verdict laid on top of it. So good and bad are real, and they are located: they live wherever there is someone for whom things can matter.
That is neither a cosmic decree nor a matter of taste. It is a fact about conscious beings, and it gives morality a floor without needing anything above the sky.
Morality that would hold with no one for anything to matter to is empty by construction. With no viewpoint anywhere, there is no mattering, so there is nothing for such a rule to be about. That is the shelf religion and natural law try to fill, and it stays empty.
What replaces it is not a free-for-all. Some principles hold for any being things can matter to, whoever and wherever they are. The central one is plain: do not pointlessly destroy what matters to someone. It binds without a heaven to enforce it, because it is keyed to the one feature every such being shares.
If you left religion and were handed a choice between borrowed commandments and "nothing really matters," this is a third option, and an honest one. It rests on a single assumed premise, stated openly: if something matters to someone, that mattering is real. From there the rest is built, not decreed. You can disagree with the premise. You cannot say the account hid it.