[simonh]

It seems to me that probably the outcome of an election should mainly be determined by the decisions of voters, not mainly by how the voting districts are drawn.

Imagine that a few voters in each district change their minds, some from each party switch to the other. Even if the overall effect is a very slight swing towards red you could still end up with all the districts going to red. Or with the same swing but distributed differently you could still end up with blue winning (though not by as much), even though it had fewer total votes.

So it's not about what should happen in any one particular snapshot. That's just a single example. It's about how well the outcome of a series of elections should reflect the wishes of voters as a whole. I'm not a big fan of proportional representation, it has often lead to small minorities gaining kingmaking powers, but I do believe that the objective of electoral districting should be to produce results that are likely to fairly represent the wishes of the electorate.