I can be an arbitrary authority against arbitrary authority right? So according to me, I am me and others who impose are arbitrary imposing values.
Since you dismiss 'arbitrary' critiques on the basis of being arbitrary alone, no. You can't, unless arbitrary hypocrisy is a social value for your universal morality.
If arbitrary is inherently self-disqualifying, then the only valid positions will be non-arbitrary sort, which must be able to be demonstrated and not simply assertion. Assertion alone is arbitrary- demonstration requires logical proof.
So my morality is the product of theirs.
But you've dismissed their morality as inherently flawed and un-true. If your morality's foundation is the output of false and erronious arbitrary assumptions, it itself will be arbitrary and false.
Everywhere in the world, every society, every inch, people impose morality on others arbitrarily, so how can anyone honestly say "It's all relative?"
By not presuming that their own morality is the only valid one in all respects deriving from some unquestionable legitimizing source, and respecting the differences in moral judgements of others where possible (and not too far outside the acceptability of the viewer's).
Show me a person or place in the world where that is not so, then what you say matters.
You have this backwards- you're the one who claims there's a universal morality out there being practiced by vague, undefined groups that the rest of us are ignoring. Having made the exceptional claim, it falls on you to demonstrate it exists.
My position is that your claim of a higher, truer, more universal morality isn't- that it's the same sort of moral posturing that plenty of other groups do. Claims to exclusive universal truths, higher morality, and dismissal of outsiders as ignorant, even willfully, and pitiful to boot are classic social conditionings to religions and ideologies... and cults.
Hardly unique, and hardly universal.