Your argument fails because 'social criticism (peer-review), observation, experiment, comparison' are, no matter what humans, however 'distinguished' might like to think, only objective in comparison to normal subjectivity, not ACTUALLY objective. In fact, since none of us are God, it can be argued that no such thing as objectivity actually exists UNLESS you 'accept the word of God' and enter that it in your everyday subjectivity. But if 95% of people aren't doing the same, you can see how that comes undone, like a popular band going out of fashion.
For the sake of convenience scientists might say that , because every time such and such persistently happens, this happens, we'll call that a scientific law unless it stops happening.
But, in morality, it is arbritary or learned choices and circumstances that sometimes result in persistence.
For example, if a railway station puts up a sign saying 'Do not stand in groups of more than 3 people', it might become the norm not to do that even though everyone was perfectly happy to stand around in groups before the sign went out and in fact even encouraged doing so because most people found it helped social cohesion.
And if the sign ended with 'Fine £1000' the hatred from others might be even greater. It's as if any bystanders gain extra pleasure from imagining that a simple 'Please disperse' from the station master would be accompanied with a penalty plucked out of the air but 'authorised' by the fact that it is on a sign.
Possibly part of the bystanders equates this kind of situation with what they regard as a similar one such as a company calling a residential phone number that's registered with the Telephone Preference Service.
Yet what they fail to take in to account is that, unlike that kind of rule which is designed to stop people's daily lives being interuppted for business pruposes, the railway station's sign might have no moral force intended behind it other than 'always obey signs'. The station master might have no moral or practical obejction to people being in groups at all but just realised that it could be a way to raise funds for the station through fines.
There are certain things that seem strikingly so wrong, such as murder, because their consequences are so final.
So why, in a war, are the winning countries allowed to, relatively carte blanche, attack other countries, killing civilians 9as long as it is from on high such as a bombing , inclusing nuclear bomb) who have not been individually asked as to whether or not they support their leader? Perhaps there are different laws allowed in war. But, in that case, cannot it be seen that perhaps there should sometimes be allowed different laws in so-called 'Peace'? (So called because some people have psychological wars to fight every day of their life to do with other people's views and expectations of them). The action is sometimes not as bad depending on who is doing it and from what short or long term mindset. A short term 'bad' could be done for the sake of a long term 'good'.
If we think of morality as fixed then the danger is that yesterday's law in favour of liberalism is somehow now regarded as the 'conservative' thing to do. Even though the original law was not meant to encourage it that is how it has ended up in the hands of people outside of high government.
Some universal laws I'd have:
'Don't enter something (including a person whether it be sexually or with a weapon) without permission',
'Don't make somebody unnecessarily fearful of you'
'Don't assume that your aims are the norm. Even if you hold them passionately you must realise that not everyone is as passionate as you and, if that proves to be an annoyance to you, you must display- or feel- in practice why your way is better in the hope that they might come round to your way of thinking if that is what you want'
'Don't assume that doing the same as what you've always done - or alternatively radically changing what you've always done- should not have diminishing social returns depending on your outlook of what those are. If you are old you are not necessarily wise so do respect the wise however old they are'
'In human terms, only you are guaranteed to be with you, so try to make sure that it is in some way a continual pleasure to be you in terms of the places and people you surround yourself with and, for your own and others sake, for that not to be at the expense of the pleasure of others'.
'Don't ignore or destroy unless an explanation for why you are doing that could be regarded as reasonable by a very sensitive person'.