Do we really want the laziest people, the dumbest people deciding our country's future? Of course not.
Maybe forcing someone to get up off their couch on voting day is a decent proxy for making sure voters actually care enough to inform themselves slightly more than the most ignorant people in the country.
If a person has a certified non-mental, physical-only disability, then we can talk about how to handle that. There should be hoops to jump through to get such a certification for voting purposes.