In fact some States (e.g. WA was like this) only allow voting by mail. Potentially disenfranchising perhaps; how do I vote if I'm homeless?
"Convinced that the people are the only safe depositories of their own liberty, and that they are not safe unless enlightened to a certain degree, I have looked on our present state of liberty as a short-lived possession unless the mass of the people could be informed to a certain degree." --Thomas Jefferson
Case in point, at least two HN readers (OP and myself) didn't know homeless people could vote by mail at the US Post Office, but I know at least one of them is very well-informed on the issues.