Like, WHY oh WHY did Joss kill Wash?

Like, someone must have an answer for this senseless death.

Especially if he wants to continue a franchise/series/whatever.....

C'mon guys and gals, put me out of my misery. Help me here.

PS. Even Book's death seemed - well, "trivial". I know in real life, it can seem like that - and the survivors spend a lot of fruitless time trying to work out the reasons why, when there probably aren't any reasons - but damnit, WHY?