Prompted by my old friend Geoff Hoff, I checked out current state constitutions for mental health and IQ restrictions. Finding the voter qualifications wasn't as easy as it sounds. In some cases, even finding the constitution was a challenge because the state website was such a mess. In some, the problem was finding the right section in the constitution once I managed to find it the constitution. There were two main reasons for that. First, was that many constitutions are not indexed; I had to start at the beginning and skim through it until I found the right section (word search wasn't much help because different names are used for voters in different states). Second, the location of the voter qualifications section could be anywhere in the constitution. In a surprising few, it is located in the bill of rights, where I would have put it (shouldn't voting be a basic right in any polity that calls itself a democracy?). In most, there is a seperate section on elections. Vermont has no voter qualifications section that I could find. Oklahoma leaves it to the legislature to decide. Alabama rather famously has the longest constitution of any state (almost a thousand sections and amendments often dealing with the most trivial local government issues).
What I found was that eight states still use the "idiots or insane" language. They are Alabama, Arkansas, Delaware, Iowa, Kentucky, Mississippi, New Mexico, and Ohio. Most of the other states have adopted more genteel language (non compos mentis and mentally incompetent are the most common). About a quarter of the constitutions hint at some kind of process for determining when someone's mental condition disqualifies them from voting (usually it runs along the lines of "judicially declared mentally incompetent"). For the most part, all that has changed is the language; the attitudes remain the same and exhibits a simplistic us and them treatment of complex mental health issues. They divide the population into a majority of sane, normal people and a scary minority of abnormal people who are idiots or insane.
Anyone familiar with mental health issues will see that there is still quite a bit of arbitrariness in the system. Although things have improved since 1902, we have a long way to go before we have a system that is nuanced enough to be fair to the whole spectrum of mental ability and health.