RandyMower via (https://creativecommons.org/licenses/by-sa/4.0/deed.en) Wikipedia Commons
If DC were to become a state they could manipulate congress to a wild degree. Those who go to work in Washington would be subject to new rules and regulations. Understand that Democrats control the DC area and the surrounding states and they would use this new power to further their political agenda. This is not exclusive to Democrats, if Republicans had the ability to get this power they would. In the spirit of the nation's founding, no political group should obtain this much authority over the capital of the entire nation.