It is never that simple. Voting by mail only works for people with reliable mailing addresses, mooting the homeless vote. At best, the US needs a combined system that will allow everyone the chance.
All these GOP schemes to prevent voting fraud or reduce costs all seem tailor made to reduce turnout of groups that are presumed to be largely non-GOP.
There is a segment of both parties that feel that people who disagree with them shouldn't have a voice - unfortunately it seems this segment managed to get a lot of control in the GOP while on the left side they mostly get relegated to the loony bin.
Both parties are super guilty of gerrymandering, but "voter fraud" isn't a proportionally important issue and it's been abused by some strategists to implement wide spread voter discrimination.
1: https://en.wikipedia.org/wiki/National_Voter_Registration_Ac... 2: https://endhomelessness.org/homelessness-in-america/homeless...