a conviction resulting in a prison term can prohibit you from ever getting a job...
Close, but not exactly. This is where the distinction between misdemeanor vs. felony comes into play. Misdemeanors (jail time up to 1 year) typically do not result in forfeiture of civil rights (you still get to vote) but may result in loss of privileges (as in losing your taxi license from a misdemeanor recless driving conviction). Felonies (any jail time over 1 year), on the other hand, you are absolutely right, these result in significant penalties (loss of job opportunities, can't vote, ...) long after the sentence has been served.
This explains old TV shows where I didn't understand why the judged sentenced someone to `a year plus a day'. That extra day turned the punishment into a felony.