First, if Assange did not violate the law of the US, then there is no cause for extradition. And so it does make sense to be talking about the US legality at this point, since USG going against its very own charter indicates that he will not receive a fair trial.
More generally, the United States Bill of Rights is framed as listing natural rights that everyone has. Yes, NSA is violating your US fourth amendment rights, despite you not being a US citizen. YMMV with practical enforcement though.
The Declaration of Independence went further, "We hold these truths to be self-evident, that all men are created equal; that they are endowed by their Creator with inherent and inalienable rights; that among these, are life, liberty, and the pursuit of happiness"
However, no legal guarantees of rights are made in the declaration.
https://scholarship.law.georgetown.edu/cgi/viewcontent.cgi?a...
Applying Nigerian law to people who aren't citizens of Nigeria would rightfully be questioned. The USA is not exempt from that. Just because it's illegal in the USA doesn't make it illegal everywhere
You'll get 100% agreement from me on that, and for example I think the ongoing promulgation of global US jurisdiction using USD as a wedge is a travesty.
But we're discussing human rights and restrictions on government, not what the US has declared illegal for US persons being applied to non-US persons. We're really talking about applying US law to the US government, operating abroad.
But we should hold our governments to the standards they are purportedly founded on, rather than buying into the justifications that they themselves have created. The opportunities to concretely do this are rare, but extradition trials being judged by a different government are one of those places.
Most US spying programs violate the 4th amendment. And have been ruled Constitutional as long as the targets are not US citizens. And if you want to seize someone's assets, you just sue the assets. The owner has been ruled to not have standing to object. See https://en.wikipedia.org/wiki/Asset_forfeiture for more.
Despite our law enforcement and government swearing to uphold the Constitution, it seems to be more useful as toilet paper sometimes.