Voter fraud can and is a real problem. It is not right to rig or try and trick the voting system into your favor, that leads to getting someone corrupt into office or leads to the citizens being very unhappy with the choices that get made and wanting to do something about it.
Yes, voter fraud is a real problem, because there are little checks on who can vote. Anyone can claim that they are a dead person, and simply fill out an affidavit that they forgot their operator's license. There are few checks on the people who run elections, and many of them have political motives. There is no way to make sure it is fair.