The constitution is written to protect the people from the government. Whether or not it should still be taken at face value is another conversation. The reason a felon cannot vote but can run for office is to keep legislation honest and prevent, for example a power hungry sitting president or any official, from passing laws that would be used to incarcerate the opposing candidates. It's to keep Trump from saying anyone with a last name rhyming with riden is a convicted felon and cannot run for office. It's what Putin does year in and year out.