Unlike lawsuits, no one has to prove they're a victim to have standing to make things illegal. But I think your statement is missing the point of the Constitution: there's a process for passing laws as long as they don't contradict the Constitution. Contradicting the constitution is meant to render a law illegal. Laws that would infringe on freedom of religion should have to go through the process of being constitutional amendments, because the Constitution is the standard against which the legality of the law itself is judged. You can't say that other laws are the standard against which the 1st amendment is judged, because that is indeed effectively nullifying the amendment. It's like saying you have freedom from unreasonable searches and seizures, except that an executive order says that all Muslims must carry documentation and submit to searches when ordered by law enforcement, because hey - that's the law now. If you can do that, what was the point of the Constitution in the first place?
Obviously the constitution cannot be interpreted in such a way that allows human sacrifice.
The laws that religious practice must obey are necessarily otherwise constitutional laws. Otherwise the law has NO WAY to distinguish if you have done harm. There is no other standard to gauge harm. Civil law is no exception. Civil disputes must still be resolved with legal arguments, and the laws in question in those legal arguments must be constitutional.
Furthermore, allowing the free exercise of arbitrary religious practice means that all laws are a violation of the first amendment, since any law would be furthering one church's religious interest provided they added doctrine to nullify the law.
I guess where I disagree with you is that I don't think civil law can be the definition of "if someone has been harmed". Otherwise there really is no point to these parts of the Constitution. Among other things, the Constitution defines things that they can't make a law against. Don't you see why the law can't also be the definition of what the exceptions to that amendment are? That interpretation is literally saying "you can't make a law against X unless the law says X is against the law". It's circular logic. I get that it's a tough line to draw but that makes zero sense as the line.