Earlier quoted context omitted.
Because I might be turned down for a job or apartment or loan because of my political views ? And because it's frankly nobody else's business how I vote ?
Voting is an inherently public, civic act. It's not a personal matter. Your vote has a direct effect on lots of other people. Why shouldn't you be accountable for that?
Your boss happens to be a friend of the candidate, or a member of a political party. You are told to vote a certain way or lose your job.
You are turned down for a bank loan because your bank manager doesn't like liberals.
You are refused an apartment because the people on your street don't like conservatives.
You fail at an interview because the interviewer only likes people who vote the way she does.
This is so bloody obvious it shouldn't need to be spelled out. Secret ballots are secret so that people can exercise their democratic rights without fear of discrimination, recrimination or intimidation.