Dems should not run any candidates in AL, AR, TN, NE, OK. All Safe R states.
All that would do is depress turnout in races where Democrats might actually be competitive.
How so? Democrats aren't competitive in any of those states in the slightest. Bronz is right, they shouldn't bother running candidates in any of those states (they'll just end up wasting resources, even if not that many, on states where they stand no chance) and should focus on actually competitive races (AZ, GA, WI, PA, NV, maybe NC).
No one should run unopposed in a general election. Should Republicans not run candidates in California or New York?