To the extent that VBM increases turnout in Oregon it does so by retaining voters who are occasional rather than habitual voters. Further, these voters are demographically similar to habitual voters. In other words, VBM does nothing to expand the electorate in ways that make it more representative of the voting age population. In fact, as MIT political scientist Adam Berinsky writes: “VBM in Oregon accentuated the stratification of the electorate. Specifically, VBM mobilized those already predisposed to vote—those individuals who are long-term residents and who are registered partisans—to turn out at higher rates than before.”I am aware that VBM here in Texas has more problems with fraud and illegal influence than at the polling place. On close elections those mail-in ballots are heavily scrutinized. Some are rejected if in the opinion of the ballot counters the signatures don't match. Some should be rejected for that reason but not all people have only one way of signing their name. Some should be rejected because the candidate or a representative provides the ballot and is there monitoring and guiding the voter as it is filled out and then mails it for them.
All voting systems are not perfect, one way to have more fair elections is to have better non-partisan people running the elections. As it is, the dominant political party in a county makes sure they put the most partisan establishment politician in the office that runs the elections.