Why does the Doctor blame Rassilon for the Horrors of the Time War?

Question

In Doctor Who (2005) S9E12, the Doctor is hell bent on (among other things) chasing Rassilon off of Gallifrey. An exchange between Ohila, the High Priestess of the Sisterhood of Karn, tells Rassilon that

The Doctor does not blame Gallifrey for the horrors of the Time War.... He just blames you.

As far as I can recall, the only televised mention of Rassilon in the Time War is his plan to enact the Ultimate Sanction during the End of Time. While this would have been the greatest horror of all, the Doctor successfully thwarted the plan, and beyond causing his regeneration, had no real lasting effects.

Is there any canon material, or material in extended universe publications - novels, audio adventures, etc, that explain the horrors to which Ohila is referring, and why Rassilon in particular is blamed for them?

Answer 1

While never stated openly, it appears that Rassilon lead the Time Lords down a dark path where the ends justified the means and all sorts of abominations (we're never shown them) were created. Things The Doctor himself feared. In other words, they became just as bad, if not worse than, the Daleks. In the episode The End of Time we see that Rassilon, ready to sacrifice the entire universe just to preserve the Time Lords. From The End of Time transcript

MASTER: But this is fantastic, isn't it? The Time Lords restored.
DOCTOR: You weren't there in the final days of the War. You never saw what was born. But if the Timelock's broken, then everything's coming through. Not just the Daleks, but the Skaro Degradations, the Horde of Travesties, the Nightmare Child, the Could-have-been King with his army of Meanwhiles and Never-weres. The War turned into hell. And that's what you've opened, right above the Earth. Hell is descending.
MASTER: My kind of world.
DOCTOR: Just listen! Because even the Time Lords can't survive that.
RASSILON: We will initiate the Final Sanction. The end of time will come at my hand. The rupture will continue until it rips the Time Vortex apart.
MASTER: That's suicide.
RASSILON: We will ascend to become creatures of consciousness alone. Free of these bodies, free of time, and cause and effect, while creation itself ceases to be.
DOCTOR: You see now? That's what they were planning in the final days of the War. I had to stop them.

Answer 2

Some prose evidence of Rassilon's guilt:

The Doctor took Cinder to Gallifrey in order to warn the Time Lords of the Daleks' plan. The Doctor told Rassilon and the High Council of the Daleks' plan, and Rassilon decided to use to Tear of Isha to wipe the Dalek presence from the Eye, killing all other life in the area in the process. The Doctor was against this plan, so Rassilon had him and Cinder thrown into a prison cell.

Also

the Doctor and Cinder escaped to the Death Zone in order to find Borusa, whom Rassilon was using as a possibility engine to predict the outcome of battles in the War.

Both from "Engines of War" (Novel)

So here we have to concrete examples of direct actions taken by Rassilon that The Doctor would of course find repellent. We can infer that there were many more which Rassilon was at a minimum aware of if not directly behind.