A good therapist directs couples therapy so that it doesn't turn into a bash-fest. It takes two and as Dr Phil likes to say, "No matter how thin you make it, there's always two sides to a pancake." Each of you are contributing both to the positive aspects of the relationship as well as contaminating it.

It may not be so much an issue with you each airing out your issues in so much as your therapist is not well equipped for couples counseling and you should consider a different counselor.