I agree. That's why I try to make clear that my "objective" ethical judgments are only "objective" within the framework I have subjectively arrived at through my own personal emotions and values. Consensus merely confirms or denies what I already hold to true within my subjective framework. In the end however if you arrive at a different subjective framework than I do, the "objective" judgments you make within that framework will be different than mine.
So essentially you are correct. Each person arriving at a differing subjective framework, might make differing objective judgments with respect to their framework. So are they really absolute? No. Not outside of their subjective framework.
The points you bring up are exactly why I disagree with Rothbard's assessment that "natural law" is the objective truth (with respect to no framework - just 100% objective and therefore absolute). Self-ownership may or may not be an objective truth (given your conclusion on the brain vat problem) but the value of the sovereignty that comes from self-ownership is a purely subjective argument.
Your points are exactly why I thought it so important to have one whole post dedicated to establishing that all ethical judgments are truly subjective at their core.
Yes, in fact, it goes so far as to the point where a central thinking problem we have in our world comes from the convenience of using absolutes when none can be grabbed onto and held in the real world. But this is not relativism, but rather, consensus building. Once enough confirmations are on the blockchain, the 'truth' is considered to have been recorded.