Morals are a mental artefact, therefore subjective?
An extraordinary assertion. Take per example your ability to read, extract meaning and respond to a post on this thread. Apart from the physical act of typing ( and neurologists will question even that) any such process/processes can be described as a mental artefact/s. If therefore we take your assertion as given, your response is subjective and therefore may be dismissed.
Whilst realising this is a discussion forum, which has rules, and one of the rules is to stay on topic, it's possible posters hold differing notions of what that topic actually is.
For instance, the central term 'morality' can be defined in many different ways. For instance, many streams of Christianity regard particular practices we indulge in our bedrooms as subject to strict moral rules whilst others claim such behaviours are outside the province of moral consideration.
Or to put it as Ronald E Merril does in describing Ayn Rand's theory of concepts in his 'The Ideas of Ayn Rand' (pub'l Open Court1991 Page 94)
"Is there such as thing as a correct definition of a concept? The most commonly held modern view is that there is not; a definition is an arbitrary convenience. This ' nominals/conceptualist' or Humpty-Dumpty school of thought holds that definitions need only be consistently maintained during a particular discussion. Just as Americans drive on the right side of the road, the British on the left, a concept such as 'bird' may be defined as a feathered animal, or as an egg laying animal. As long as everyone who is using the definition ( or the road0 agrees to accept a particular procedure, the exact procedure chosen is of no importance.
Opposed to this is the 'realist' school of thought, in it's pure Platonic or diluted Aristotelian variants, which hold that there is only one correct definition of a given concept. What though, could give this 'essence' of the concept it's special validity? The 'essence' is real in this view - it actually exists, as a Platonic form or some such entity.
Rand rejects both these approaches. As she describes it, the nominalist regards definitions as arbitrary; there is no 'essence' of a concept. The realist postulates the actual existence of the essence; essence is metaphysical. For Rand, definitions are not arbitrary - there is and essence -but the essence is not metaphysical but epistemological. Though concepts are in the mind, they are not arbitrary because they reflect reality, which is objective.
Now, why should anyone bother with all this? Rand's answer would be that philosophy is practical. The nominalist view assumes the thinking is a matter of detached, abstract debate. It is a game, and the only requirement of the rules is that they be self consistent and agreed by all players.
But for Rand, thinking is man's means of survival, and it's rules are absolutely critical. If you pick the wrong way to define a concept, it may not just be 'Well, that's an interesting way to look at the subject'; it could kill you. "