Why Blood > Frost (Tanking)

There seems to be a bias when it comes to a Frost DK's capabilities as a tank, in comparison to that of a Blood DK's. A lot of this stems from an underestimation of Will of the Necropolis. Let's compare the passive effects.

Improved Frost Presence (2% DR) vs Will of the Necropolis (15% DR when under 35% HP)

WotN is almost, but not precisely, functionally similiar to having a 5.25% DR for the whole 100% of your HP. That's just a different way of evaluating the talent. As you can see, WotN basically flattens Improved Frost Presence. Then we have the cooldowns.

Unbreakable Armor (+ Imp Frost Presence) vs Vampiric Blood (+WotN)

Assuming the best case scenario for UA (taking you from near 40k armor to the armor cap). This would result in a physical damage reduction of around 15%. This is on top of your passive effect from Improved Frost Presence. In terms of EHP, the effect is comparable to that of Vampiric Blood + WotN, however the latter actually assists with spell damage too, and the healing increase it offers you is amazing. The only advantage of UA is that it lasts 5 seconds longer, which isn't all that enticing when you're measuring it up against an alternative that's better suited to more situations.

Based on the difference in passive effects, as well as cooldowns, Blood is almost always better. Whereas Unholy tanks have some very clearly outlined niches (like aoe threat+dps, and the ability to pre-cast bone shield well in advance and have it come back up right after it falls off, which is advantageous on bosses where you have downtime as a tank like Sindy), Frost is mostly eclipsed by Blood thoroughly.

As a final note,
1 + 1 = 2

Exactly as expected from an exploiter. Shame on you for misleading people.
Oh, and, 1 + 1 = 1.9999597368 (When adjusted for "curves in the spacetime")

I'm pretty sure the majority of players already agree that Blood is better for ICC when it comes to boss tanking. When did these Frost activists suddenly emerge to slander the name of Blood with their bias in order to warrant this thread?

Yeah, you basically hit all the main points. Especially about WotN; so many people are way too quick to dismiss the talent out of hand without fully appreciating how immensely powerful it really is. As for Frost DKs, some parallels to the Protection Warrior can be drawn here - more promised damage mitigation, yet ultimately the spec is set back by its noticeable EHP inferiority, along with having a spec-defining cooldown that only covers you against physical damage. The damage reduction tools Frost has are its main allure, but when you consider those damage reduction effects in terms of their effect on your EHP, as opposed to simply looking at them in a vacuum, you see how they don't really compare to what Blood has to offer.

Some other points I'd add:
- UA and IBF lasting longer, while clearly being things a tank would be grateful to have, don't necessarily provide enough niche use in and of themselves to be sufficiently compelling for you to want to forego Blood's WotN most of the time. If you can find a terrific use for the +6 secs of IBF, then we have a different story.
- Acclimation also tends to be tremendously over-rated. One major drawback of this talent is it provides you with resistance against damage only after you've already been hit. For that reason, contrary to popular belief, it barely helps on Sindragosa and doesn't really help on Keleseth either because his Shadow Bolts aren't partially resistible on 25hc. Infest on LK procs it, but doesn't stack it, due to Acclimation's 18 sec duration whereas Infests are spaced 20 seconds apart. One use that occurs to me is getting good uptime on it in P2 of heroic LK, from the Soul Siphon casts done by the Val'kyrs in the air, since Soul Reaper's initial hit is partially resistible. But even there, it's at best just a flimsy band-aid for UA not being able to render magic damage assistance in the first place. It probably shouldn't proc off Halion's aura in the Shadow realm either, though it might be worth placing a source for whether the fire hits from the Living Infernos and Embers should or shouldn't proc it.

Overall I'd agree with the conclusion that Frost is quite thoroughly eclipsed by Blood. Unholy on the other hand actually tends to retain most of its usefulness in the vocations that can be considered its mainstays, to reiterate your point. Stuff like being able to throw up a Bone Shield well in advance before taunting Sindragosa, and then having it come back up again just as it falls off so to achieve higher overall BS uptime - basically using tank swaps and boss downtime to game Bone Shield's mechanic to your advantage in ways like that. The AoE DPS (and threat) will also find use on Halion 25hc. Speaking of Halion, there's also the spell EHP superiority which is also going to be a great help if you're off-tanking in RS 25hc because spell damage will be all you take.