I really like the Uchiha's, maybe more than any clan. So the following is not a hate comment.. but...!
They are all a bunch of Emo's.
But the story around them makes a lot of sense so i like this. If you love things very much it will indeed be missed even more when gone. Imagine losing someone you love.
Now if this tremendous love feeling exists in them, of course losing that will make them too sad or angry to live. I think with Izuna's death Madara really turned into the dark zone. Obito loved Rin most of anything at the time, as why he turned dark. (also, i finally understand why he wasn't all Saiyan-Like cool when he was young)
Sasuke turned dark when losing his brother. Itachi wanted him to hate Itachi and not love him too much. So that Sasuke would never fall in that darkness, but in the end he did. Even more because he found out. I think this is why Obito told him the story in the first place.
Last thing i'd like to say; is that i now understand the soft personality of Zetsu. And the goofyness of the goofy one that befriended with little Obito in Madara's cave.
They're truly clones of Hashirama