Morals, like their fully ritualized and institutionalized cousin, the "law" of the "state", are too often mixed up with ethics, while in fact, they for the most part are the exact opposite of ethical.
Morals, law, fashion, customs, traditions, etc all are indeed arbitrary, currently adhered-to thoughts and habits shared by some (actual or just purported) majority in a social group.
Ethics, on the other hand, looks for fundamental, objective measures of what responsible social behavior means, with the intend to follow it for the best of all.
The key is to understand what life is, as opposed to non-life: negentropy, the withstanding, overcoming and outwitting of the physical tendency for structural decay and information loss over time. That is the essential meaning and purpose of life as such.
Intelligent life, and this currently means humans on our planet, has the meaning and purpose of furthering the general meaning of life actively, consciously and wisely, to maximize negentropy.
Anything that is entropic, that destroys, kills, harms, etc is bad.
Anything that is negentropic, that gives birth to, protects and supports life, is good.
Any actions of humans that are bad by intention, are evil.
It is as simple as that.
If an action would have a primarily negentropic result, it is unethical and thus should be avoided.
In every life situation, try to find the path of actions that minimizes the likelihood of entropic results and that maximizes the negentropic outcome.
(written 2019-01-08)