One thought on that matter is that sometimes (often) the...... "What? What do you need that for?" response is an emotional reaction due to the other party feeling threatened or trying to sort out what you think is wrong with them. It is a fear centered question / reaction. Rarely is someone oblivious to problems in a relationship.
I am guilty as charged when it comes to that as I was approached about my spouse who wanted to go to a counselor during my drinking days. I reacted with panic- Why, what's wrong, why do you need to do that....on and on. I wore her out with questions. It actually caused her to drop the issue and not seek what she needed; further driving a wedge between us until I finally got sober.
Your spouse is probably threatened or worried about what might come from counseling. Maybe rightfully so and maybe that fear is unfounded....but fear is fear and it causes reactions.
My suggestion would be to go and invite them to attend if they want....but cheerfully go regardless of their attendance. Most people will, at some point or another, decide they need "representation" if there is a meeting about the family / marriage and will acquiesce.
The one exception would be a narcissist who has been called out before, or has an inkling that they may be called out in general. They tend to avoid any outside party that might see things through a clear lens and not agree with their altered perception.
Approach your spouse in a loving way, tell them you are going, you think counselling will strengthen the relationship, and tell them they are free to attend if they want.
Either way you'll get some help....maybe as a couple or maybe as an individual........ but seeking help isn't wrong in this situation.