So? That something bad might happen doesn't mean that something else shouldn't be done, but simply that you should design, test, adopt and perfect a system of checks and balances to deal with whatever issues might arise, provided that you consider that the benefits outweight the costs.
Then you factor that republicans would cockblock it anyway and just keep getting reamed in the midterms.
Democrats and Republicans alike have been creamed* in the midterms for the last couple of decades anyway due to the "out of power" "punish in power" party phenomenon we have.
http://www.centerforpolitics.org/crystalball/articles/house-2016-clinton/
http://www.centerforpolitics.org/crystalball/articles/explaining-the-republican-lock-on-the-u-s-house-of-representatives/
Those too articles explain the reason. Turnout certainly affected the Democrats in 2010 and 2014 for sure though.