Classic sophistry.
Today that might be true.
140 years ago? Only a fool would dismiss the important role of the obvious cultural and historic context.
Ethical and moral time machines are only a useful tool against the ignorant and the unsophisticated.
It's not a time machine. There were people at the time who routinely disregarded the fugitive slave laws because those laws were unjust. Were those people wrong?
Will an up-to-date example satisfy you? Suppose I see a knife-wielding assailant attacking a child behind your screen door. I come on to your property and fend off the attacker, but you call the police to have me arrested and prosecuted for trespassing. The prosecutor prosecutes me, and the judge strictly instructs the jury on the elements of the crime of trespassing. Should I be convicted?
Cordially,