It is so much easier to get a hundred people thrown off the voter rolls because they have a name like say, Martin T. Johnson, that is similar to a person named Martin J. Johnson in jail, then to get a hundred ex-convicts-- who have had their voting rights restored-- registered to vote.
And challenging people at the polls? This is so low--these are people who 1)went to the trouble of getting registered, and then 2)found out at least something about the issues, even if only the name of the person or party they prefer, and 3)showing up, possibly waiting in line, to vote.
The more steps you put between a person and the ballot box, the fewer will jump all those hurdles to vote. Marketers know this and try to make it easy peasy to buy things. Amazon has you register once, select a PIN and then you can order with only one click. Voting should be something like that-- isn't voting more important than buying stuff? We have the technology for people to be able to have a secure PIN so that nobody can vote twice, and there are ways of making sure the person who is voting is who they say they are--DOB, social security, mother's maiden name, first pet's name, favorite Monkee or Beatle, whatever. Online banking does this all the time.
If you are a citizen and over 18, you should be able to vote from any computer and at any time of the day or night, from say, a week before the election. And the rules should be standard from state to state. Is seems unconstitutional for a person to be allowed to vote for president in one state and not if they relocate to a neighboring state because of different ID requirements, different rules regarding felons, etc. Equal protection much?
As the numbers of people voting dwindles, you get more extremists, one-issue voters and partisans-- the people who really care about politics. Because people with less fervent attitudes and better things to do don't participate. Eventually most people stop paying attention to politics and try to survive as best as they can. All that no-government, local community, rugged individual thing that we in the US admire so much.
And that is how we could end up with a dictatorship where everything is taken over by a handful of people. Which would be bad for everyone, whether the dictator comes from the left or the right. Both types control the economy and all information and throw people in jail for thinking the wrong way.
Although I have to admit that I prefer a dictatorship like Cuba and China that tries to feed, house and give medical care to everyone, to one that just steals everything and shoots people, like in Guatemala and Haiti. I have lived in two dictatorships (both right wing, the very popular "steal everything and shoot people" kind) and it is a very scary thing to have to watch what you say in public at all times.