greg palast has often argued the opposite position, and does so here.
but, the united states has a very long history of electoral fraud, and stuffing ballots is how they do it. jfk, for example, stole the election in 1960 - as bush did in 2000.
trump may only be accidentally half-right, as is so often the case. but, it's the kind of thing that people should actually be taking very seriously, if they're concerned about electoral integrity.
if you want your vote to count you should walk it in.
and, if you don't want the political class rigging elections, you shouldn't hand them the opportunity to - an opportunity they will take, if you give it to them, because they always have.
https://www.gregpalast.com/rush-to-vote-by-mail-could-cost-dems-the-election/