No, I wouldn't want to know. I'd end up lying in bed awake, worrying about it, fearing it, especially as the date drew nearer and nearer.
Plus, you'd have the dates of your loved ones' deaths on your mind, too.
It sounds like a way to just be continuously sad about someone's imminent death.
And, for example, my dad was a living kidney donor for my uncle. Would it have affected his decision if he'd known my uncle would die on transplant day? Or a few months' later? (Fortunately uncle is still going strong.) Would other donors be convinced not to donate if they knew the recipient would for shortly after? Would they see it as a waste?
And what about dating? Would it become the norm for people over 21 to ask their dates their death day? Could you imagine having a death date 5 years in the future, so no-one wanted to date you because there was no longevity? Would you end up with a two-tier kind of society, with those who have long lives ahead of them enjoying everything life brings, but those with a soon death date grouping together in these kind of supportive palliative care groups?
Such an interesting question, OP!
As an aside, when I was about 23 I did one of those ridiculous online death calculators (from Facebook?). It said I would die in 2052. I'll be in my 70s. It will be interesting to find out if it's true (as in, coincidental or bollocks).