I agree that noting these particular topics is being used to weed out "apostates". It's why I always speak of my aunt who is, in real life, a JW many states away and bring up those topics as questions I have had over the years in her efforts to convert me. I never, ever mention I was ever a witness. I never mention anyone but my aunt and that has encouraged the few that engage with me over those points to applaud me for my "sincerity" and "desire for truth".
I was very good at refuting "conversation stoppers" back in the day but those 2 were tough ones that I did not encounter often and were challenging. I got the blood issue way more than disfellowshipping. I was way too programmed back then to see reason even when they brought up points I couldn't refute though.