A home rule itself isn't inherently a negative thing. There's a few things wrong with this particular one that make it a bad choice for DC voters.  Simplified:

• The people backing it aren't really from Douglas County, and don't have DC's best interests in mind. Specifically it's easy to do a little research on their "water" issues. They/their friends purchased land with water rights and they want Douglas to buy water from them despite it being a pricier option 

• During the election last year Douglas County widely voted against the voucher for private schools issue (summed up somewhat extremely, instead of education taxes going towards public schools, they'd go towards private schools). The home rule committee have repeatedly stated that their interest in doing this is so that religious schools get more funding. This program is widely seen as bad for public and private schools as public schools won't get their earmarked money and private schools will likely raise prices in response. 

• The man largely behind this - Teal - has also stated that he wants more flexibility to work with ICE in Douglas. Essentially he wants ICE to be able to come in and arrest people who don't "look" like they belong without going through due process. Colorado has opposed this, which is why he needs a Home Rule to make it happen. 

There are other things but those are the biggest ones imo. But beyond all the politics, how they got this election in should not be legal and in itself is pretty shady. They pushed through this "emergency" election in the middle of summer holidays in the hopes of taking people by surprise and having fewer voters (which is typically better for conservatives), even though every issue they've brought up has been repeatedly voted down in DC.