“mixed seating can lead to aveiros. “
And it can ALSO lead to mitzvos – that of young men and women meeting each other in an enjoyable environment, and possibly dating and getting married. I know several people who met each other at simchas where they were seated together. Of course this was in the days when people were not afraid of mixed seating leading to aveiros. They had a little more faith in the young people of that day. And deservedly so.