I don't agree. Some rights are fundamental - the people who had their lives stolen by trans Atlantic slaving had their lives stolen. Their rights were violated. The fact that the social and political system of the time conspired to facilitate that doesn't make it less true.

I think the parent commenter was trying to say that rights only exist as a productive concept when other people agree with them.

You can argue that certain rights are fundamental, but it doesn’t mean anything if most people disagree with you. Whether or not rights are “fundamental” (i.e. exist outside of an enforcement structure) not a useful distinction, because it’s meaningless - whether or not you get to exercise that right has nothing to do with your claim being correct, it has to do with other people agreeing and sanctioning your behavior.

Like most normative claims, personal rights do not really exist coherently if you don’t first define them in the context of a relationship. This is demonstrably the case because the idea of a right would be redundant or meaningless if it were not for an adversary threatening that right in the first place.

They had their lives stolen before that - they were already slaves by the time the Western slave traders bought them from their local, African slave owners.