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.
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:
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.