Mail-in ballots should be banned as they would impose added expenses and hassles to the voting process for both citizens and the government.
Both state and federal governments would incur a plethora of new expenses for a switch to mail-in ballots. Ballots and corresponding instruction sheets would need to be mass printed for each eligible voter. In addition, each ballot would need an envelope and stamp for transportation. Lastly, and most importantly, delivering the ballots to every eligible voter would add even more expenses. The costs of paper, ink, labor, postage, and delivery fees would amass to an unreasonable amount for governments. 
On the other end of the process, citizens would have new expenses with the adoption of mail-in ballots. Buying stamps, organizing paperwork, and navigating through the U.S. Postal Service adds even more impediments to an already cumbersome voting process. 
Perhaps the most significant pitfall of a mail-in ballot system is the unwieldy logistic difficulties it would cause. Very few states have the postal capacity to handle the overwhelming number of ballots in a timely manner. On top of that, mail-in ballots would need to be counted, calling for added expenses of manual labor or high tech ballot scanners. There are many errors that would happen randomly, adding to the massive hassle of mail-in ballots. 
The U.S. Government should ban the use of mail-in ballots for the 2020 election for the added expenses and burdens they constitute.