Hey Gemme!
This is totally an aside, so please excuse pyjamas.
A couple of years ago I would have agreed with you. However, after a shit ton of work on my codependany stuff, I no longer feel any responsibility for other people's feelings of hurt. Meaning, I understand that something I can say can or do can influence how someone feels, but I feel no responsibility to solve or fix or make things easier/softer for facing up to people's own stuff.
It's really up to someone else to care take their own feelings, especially if I have been estranged from them or I don't know them well.
If my "no response" is what I personally wish to do, I'm well aware this may feel extremely uncomfortable and even painful to the person making an apology. But that is their work to do, and personally, I no longer see it as any of my biz. I feel a lot healthier and happier and emotionally cleaner for it.
That someone who I no longer wish to interact with will be hurt by me not answering a letter of apology? That's ok. They can be hurt. That's their work and pain to figure out. If I am not willing to interact with them, that's just how it is. Sometimes the work is like chewing down on a cup of cold sick. If I can do it, so can they. I have every confidence in their ability to deal with it.
I know that's not quite what you ment. But I think allowing people to feel hurt and not doing things to save them from hurt is not always the best thing to do. A true apology expects no forgiveness or even acknowledgement.
I guess at the root of it I sincerely feel after a no acceptance or aknowledge ment is:
The work for them after that point is to forgive themselves and that's nothing I can help with nor any of my biz. And that's harder work than someone else forgiving you.