I think that there is a symbolic meaning to his desire to surrender his rights, and that symbolic meaning is what upsets you SO much.

Basically, the son is a product of your union. Surrending his rights to the product of your union serves to cancel out the union, retroactively. And that, further, serves to delete YOU from the conscious record of his life, and you do not like it, for a very good reason.

You also do not like that your current H prefers to pretend that there was no life before him, and sometimes you find it disturbing, and I am totally with you.

The symbolic meaning of your current H's preference to pretend that there was no life before him is an attempt to delete a portion of your life.

And you do not like that. You want to be acknowledged as a person and you want your life history to be real to everybody. You do not want people to pretend that part of your life did not happen, because it did happen, it did get seared into YOUR memory, and all attempts to delete what got seared into YOUR memory - whether by Ex or by current H - are disturbing to you and they should be so.