Vote by mail previously had to be specifically requested. This reduced the chance of shenanigans. Many of the people who speak against it are still in favor of being able to vote by mail by request.
Pros:
1. The ability to vote from the comfort of your home
2. The ability to avoid polling places. (Irvine was never a problem, though)
3. The ability to avoid people with viruses.
Cons:
1. Mail in voting encourages early voting. Early voting allows for politicians to win the election without having debates. Now, most people already are decided who they are going to vote for.
2. Pre-filled ballot mailing allows for someone to intercept and vote using the prefilled ballot.
3. It makes it easier to vote on behalf of those that you know are not going to vote.
4. Mail carriers can throw away votes from houses with political signs they disagree with. (be sure to drop off at the post office instead)
5. Mail in voting is more prone to error.
6. The number of mail in votes was lower in the past. If the votes are to be counted on election day and we were overwhemled last election, then consider how long it will take to count this election.
Concerns:
Last election we saw a much larger turnout of mail in votes. We also saw our own election results get flipped when the mail in votes were counted. That may have a rational reason, such as certain people are more likely to vote by mail. It is concerning that the vote results greatly flipped and probably caused some people to change their mind on their openness to it.