Why did Daniel drink the Amnesia potion?

[tacc]

Even though I got the feeling that Alexandre was lying about those people being murders and what not.
I think most of them were people taken from their homes or explorers with a very bad luck.

I assume that's what the letter in the Wine Cellar wanted to tell you.

Spoiler below!

My name is Wilhelm, house of Gerich. These are my final words, my confession and testament. Two years ago I was summoned to the castle Brennenburg. [...]I was to kidnap healthy humans upon his slightest whim and do so without asking questions. [...]Ever since that day I've brought men, women, and children to Brennenburg. I can't remember the numbers, but there were many, perhaps even a hundred. None of whom were ever seen or heard from again.

Though I think that could have been conveyed better in the diaries and such.

You mean like this?

Spoiler below!

[...]
Alexander, I will kill you for what you have done. If only the Shadow had caught me in London or Algeria I wouldn't have to suffer this humiliation. You made me a murderer, a monster!
And now, I merely await my death. I am too weak to press on. I can hardly stand as my knees fail me. I cannot see as my eyes are dressed in tears. I am as broken as the men I have tortured. If only I could wipe my fear away as we did with them.

Solution: Forget about all these. You don't know who you are, you don't know about shadow, you don't know about servants, you don't know who is Alexander...
There yo go! Run for your life and kill Alexander.

But don't forget to scatter you Diary everywhere to remind you of what you want to forget.