gerrymandering is good--for the electorate. why?

Because gerrymandering increases homogeneity. A gerrymandered district is more homogeneous--the voters are more alike than they were before. In general.

Homogeneity in general increases unity. A more homogeneous district means the voters in general share more common interests. If the voters share more common interests then it is easier for them to elect and hold accountable a politician who can represent their common interests.

Of course if you want the corporations to have more control over the government, and you want the people to have less control, then gerrymandering is indeed bad.