Power does tempt people to abuse it, and they regularly give in to that temptation. While I'm not in agreement with the person you are arguing with, I do believe people cannot be trusted with power, and therefore there need to be checks, and recourse, and the more power a person has, the more they need to be monitored rather than trusted. (Police are an example. Politicians are and example. Hollywood producers area an example.)

There is also a selection mechanism at play. People who like to abuse power seek it out.