Okay, finally had time to check out that article you posted, Jodie, and look into neonate blood composition and whatnot.
Unfortunately that article starts out completely wrong, as far as I can tell. Newborns do NOT have thin blood. On the contrary, neonate hematocrit is normally *higher* than adult levels (45-65% being normal for newborns, adults 40% for women and 45% for men). This makes for increased blood viscosity and the exact opposite of "thin blood", and with extra blood cells cells floating around, if viscosity WERE a factor in the stem cells from the cord blood moving throughout the body (which is by no means certain, that doesn't really make any sense to me) then neonates SHOULD have lower blood viscosity, but they don't.
Secondly, vitamin K is not administered to "thicken" blood, only to increase its clotting ability. In the absence of damage, vitamin K does nothing to the viscosity of the blood - the body only clots blood when damage occurs, to prevent blood loss. Even high levels of vitamin K do not turn blood to "sludge" - hyperviscosity actually IS a recognized problem in neonates, occurring more often in pre-term and small-for-gestation babies, and can be accompanied by brain damage and other symptoms. There is no suspected link between vitamin K at birth and hyperviscosity.
The article is also pretty inaccurate about the use of warfarin and the management of vitamin K in "older people". Actually, it's people who have cardiac issues, and it's to *prevent* clots that can easily turn into strokes, and variances in vitamin K can make it extremely difficult to gauge the dosage of the warfarin so it is tightly controlled through diet so the warfarin works and does not cause hemorrhages. I am well-versed in THIS aspect of vitamin K because my mother was treated for a congenital heart defect some time ago and I helped her do the research on it so she could understand what was going on, and why she was put on warfarin and beta-blockers and why if she wanted to eat kale she had to eat it every day. Vitamin K is *controlled* not restricted through diet - patients are generally advised to limit intake but above all else, to keep it *steady* day-to-day. I don't think this is particularly actually even relevant to the discussion of administering vitamin K to babies, however, and it's a bit of a red-herring argument thrown in there besides being misleading and a bit wrong.
Now, all that having been said - I did some additional reading and am coming to think that I will probably opt to have vit K on hand but will only use it if the birth is traumatic, uses instruments, or we can't delay cord clamping for any reason.
If you want a BETTER article (despite the source) with which to argue against routine vitamin K use, I would recommend this one. I should say that I am very much not a fan of anti-vaccination organizations, however this article has nothing to do with vaccines, is well-written, and seems to be exhaustively researched (although some other time when I am not completely pooped, I will go back and have a look at the numbers and studies behind the claims that the vit K shot puts vit K plasma levels up so extremely high in neonates - that seems a bit off to me). But the rest of it is pretty good, and correlates well with the position papers of the CPS and several BC midwives (if the conclusions reached are slightly different, mostly due it seems to differing opinions and interpretations of the same studies).