I doubt anyone you are talking to is opposed to all human rights, that sounds very much like a straw man statement. Reasonable people can disagree about whether any particular right should be protected by law.

The reason is simple: any legally-protected right you have stands in direct opposition to some other right that I could have:

• Your right to free speech is necessarily limited by my right to, among other things, freedom from slander/libel, right to a fair trial, right to free and fair elections, right to not be defrauded, etc.
• Your right to bodily autonomy can conflict with my right to health and safety when there is a global pandemic spreading and you refuse vaccination.
• Your property rights are curtailed by rules against environmental harm, discrimination, insider trading, etc.

No right is ever meant to be or can be absolute, and not all good government policy is based on rights. Turning a policy argument into one about human rights is not generally going to win the other person over, it’s akin to calling someone a racist because of their position on affirmative action. There’s no rational discussion that can be had after that point.

I don’t know if it helps, but this is not really a lie, and you shouldn’t feel bad about saying it. You have your own reason for not being able to do something you committed to. Someone else might have a different reason that is equally personal that they don’t want to share. “I forgot and I’m sorry” is a socially acceptable way to take responsibility without sharing specifics and potentially making someone else feel confusion or pity.

You can still work on the “why wasn’t I able to do the thing I felt I needed to do” without worrying about “why wasn’t I honest about my reason”.

Just my two cents though.