In Athens only adult males with military training could vote and they voted for everything unlike in us citizens age 18 and above can vote and in US the people elect representivites to represents them.
That could go both ways, maybe they didnt own a plantation or have use for a slave. But they still could support it. Or, they could be completely against it, and think its completely wrong and dehumanizing, they could help runaway slaves get to the north.