I voted in the Indiana primary on the Republican side (hint: It wasn’t for Trump or Cruz) and this thought struck me as I looked down ballot. In many races, the party nominee was unopposed and there was no write-in option available. Should I, as a voter, have the right to vote for whomever I want through a write-in?
There is no doubt that states can regulate who appears on the ballot, as there could be significant administrative problems if anyone who wanted to be on at any time before the election could get on. Are there similar issues with respect to write-ins? Not really. Having a write-in option does make counting the votes a little more difficult, but that seems pretty insubstantial. On the other side, you can make a strong argument that voters should have the option of voting for someone not on the ballot as part of their freedom of choice.