IMHO, an important consequence of gerrymandering is that it makes districts less competitive. Instead of a district where neither party has clear grip (so the winning candidate needs a broader appeal), we have one which is either clearly R or clearly D. Now a candidate no longer has to care about the other team, because once your own party approves your candidacy, you are as good as elected. So party loyalty is what matters.
The result is a funnel to select fanatics over moderates, from both sides.
I don't think that's an unexpected consequence. That's the intention. Rope off the folks who won't vote for your party into one district and you get to win the rest of the districts. Or run the lines so that your opposition's support is broken up and sprinkled harmlessly amongst your supporters so that their votes are swallowed up by your supporters' votes. Then you've got no reason to actually work to improve anyone's lives and can spend your time figuring out how to leverage your position to make as much money as possible.
The Wikipedia article has a good graphic that helps visualize the strategy.
For bonus points, devise ways to make it more difficult for the demographics that are likely to vote for your opponent to get to the polls.
Exactly, all these one party districts, and states, are not great for democracies. Basically, you get institutionalized corruption, nepotism, inefficiencies, etc. Doesn't matter if it's red or blue. It's bad either way. Swapping out parties once in a while is a good way to shake things up and break that pattern.
The result is a funnel to select fanatics over moderates, from both sides.