There is only one compelling argument against "vote by mail."  It would increase voter turn-out and counter efforts at voter suppression.  Since all polling data, including exit polling, shows that the greater the voter participation, the better Democratic candidates fare; be assured GOP members of both State legislatures and Congress know this.  

Vote by mail has worked very well in Oregon....far more convenient for all, increased participation and very, very few problems.  The system should be a model for other states......With GOP controlled legislatures in many of those states, don't expect that model to be emulated.