I agree the Republican controlled state legislatures gerrymander the districts so that they can control as many congressional districts as possible. That is stating the obvious.
But Democratic states do the exact same thing! No difference at all for their motives or actions.
In New York the 59% of registered voters are Democrats but they control 77% of the congressional districts. That's because they gerrymandered them!!!
Ed Koch spoke out about this before he died. He started the non-partisan group New York Uprising, and one of their primary goals was to end gerrymandering in New York. He went to every state legislator and asked them to sing a pledge to join his group. Of course many that signed the pledge went back on their word and voted against his proposal.
I'm sure California, Illinois, etc do the same thing...
Democrats are equally evil and quilty in this respect.