Doodledog
I've often felt that home DNA kits can do more harm than good, and although I am fascinated by genealogy, I think there are issues there, too. People (including the dead) have a right to privacy (morally, if not legally) and reading old love letters, or investigating personal circumstances doesn't sit well with me.
'Surprise' babies do arrive - often in menopause - and there is nothing strange about it. If your mother had wanted you to know her story, she would have told you. All may be exactly as you were told as a child, but if it isn't, doesn't she have a right to keep it to herself?
I agree, I hate the thought of people poking through my life so why would I think it is OK to do that to someone else even if they are dead.
We have a bundle of letters my late MIL and FIL exchanged during WWII. They were a wartime romance and married when he was on weekend leave. They exchanged letters and probably some leave time he had which is likely when DH was conceived. He died when my husband was a baby, my husband grew up knowing little about him as he quickly learned that asking anything upset his mother. Reading those letters might let him know something of his father. They have sat in a drawer for over 15 years, since MIL died. We can't throw them away, she kept them all those years, but we have never read a word of them. I think it is about respecting them. I think when DH dies they will just go in the fire.