@ myles: Yes. 30's Germany is the BIGGEST reason for being swayed. No dought about it. For the necrons there "dirty 30's" was the fact the suffered short life spans.
Yes the tec was there, but even if they shielded them selfs from the ration the effects and damage would still be there on a genetic level.
Cancers and tumors being the 1st things to come to mind, and becoming common genetic defects that are passed on down.
Also if looking at tomb king fluff and the necrons relation. I would also Imagen some how they became a very "death" fearing race. They probably suffered from sicknesses of all kinds. Well again you see the Old Ones who lived long and healthy lives.
I see it as the C'Tan the the Necrontyr in the loop swaying the Necrontyr race off there feet. With promises of something better then long health lives, immortality! If they fellowed the C'tan and the lords.
The C'Tan also feared the old ones psychic abilities. So could be a reason for why they would promote and lead the Necrontyr into there hate towards the old ones.
I know in the end it's just my interpretation, and it's probly has some holes in it. But it's the best thing I can think of, and makes the most sense to me.
Realy the Necrontyr story is more like a warning tail then anything eals. About how Greed/Envy/Hate are bad and ect and so forth, then any real back ground. Witch I think is the idea since the necrons are so old there discriped as being only scary tails the older races tell to there children.