A very moving tribute to the benefits of facing death from one of my commenters:
In January 2004, my 35 y.o. GF was diagnosed with glioblastoma (the most aggressive brain cancer). Surgery was not an option, and the statistics bear out that 95 percent of patients die in under a year (she was a cancer survivor for 10.5 months).
If told the truth, you have options (including denial, which some do choose). But the truth is superior for many reasons, some of which I probably did not experience first hand. Jean got to put her affairs in order. She got to see her brother again (who would never have gotten on a plane were it not for her diagnosis). She got to grieve what she would miss, which made her (and me) appreciate the things she did not miss all the more.
A terminal diagnosis does in fact bring horror home, and perhaps the reaction you have and the desire to be lied to (assuming that's what you'd personally want), Ms. McArdle, expresses the desire to avoid that horror. I can sympathize with that. But as I said, you can always go the denial route and believe you are misdiagnosed, or you will be the outlier to the statistic (which is how we lived those 11 months).
But life in the midst of death also has a richness that I've not experienced anywhere else. You can appreciate moments of peace and moments of reflection like you may never experience again. You can touch, and be touched, in ways you probably can't empathize with until you are there living it.
You need to know that the end is near to be able to transcend the ordinary.
I have met people my age who lost their lovers to accidents and others who lost their lovers to disease over time. Without exception, the former envy the latter. We had the chance to say goodbye.
Nothing tyrannizes death like acceptance of it.
The answer is, I don't know what I'd want. But to me the greatest horror of the death penalty seems not the death, but the waiting for it.